Valve Software

Valve Software was founded in 1996 by two former Microsoft Corporation employees, Gabe Newell and Mike Harrington, and headquartered in Bellevue, Washington, United States, later becoming Valve Corporation. They are best known for developing the Half-Life series.

Games
Valve have unique way of making a video game; unlike other video game development and publishing companies, the employees choose to work on whatever projects they want to. They don't have deadlines, and they don't have managers. Most of their games were not actually made by them; Valve often hires the developers of popular mods and improve upon them, then release it as a game (e.g Team Fortress series, Counter-Strike series).

Half-Life series
The Half-Life series was a series of first-person shooter developed by Valve and Gearbox Software using the GoldSrc and Source Engines. It is Valve's biggest series yet containing Half-Life, Half-Life: Opposing Force, Half-Life: Blue Shift, Half-Life 2, Half-Life 2: Deathmatch, Half-Life 2: Episode One and Half-Life 2:Episode Two.

Half-Life
Half-Life was a first-person shooter released in 1998. The player takes control of fictional theoretical physicist, Dr. Gordon Freeman when an experiment goes wrong. The game uses the GoldSrc Engine, which is a heavily modified version of the Quake Engine developed by id Software.

Half-Life: Opposing Force
Half-Life: Opposing Force was a first-person shooter developed with help from Gearbox Software. It was an expansion for the game Half-Life and released in 1999. The game is set during the Black Mesa incident from the perspective of Corporal Adrian Shephard, a US marine. The game uses the GoldSrc Engine.

Half-Life: Blue Shift
Half-Life: Blue Shift was a first-person shooter developed by Valve with help from Gearbox Software released in 2001. It is set during the Black Mesa incident, but from the perspective of another character, Barney Calhoun, a security guard at the Black Mesa Research Facility. The game uses the GoldSrc Engine.

Half-Life 2
Half-Life 2 was a first-person shooter released in 2004. It is set after the events of the seven-hour war where humanity was enslaved by the Combine. The player once again takes control of Dr. Gordon Freeman. The game uses the new Source Engine developed by Valve.

Half-Life 2: Deathmatch
Half-Life 2: Deathmatch was a first-person shooter released in 2004. It was released separately from Half-Life 2. It was a deathmatch game using the same character models from Half-Life 2. It also has a Team Deathmatch mode, where you can choose either the Rebel team or the Combine team. The game uses the Source Engine.

Half-Life 2: Episode One
Half-Life 2: Episode One was a first-person shooter released in 2006. It was the first expansion for the game Half-Life 2. This episode takes place after the event of Half-Life 2, next to the well-worn Citadel. The game uses several upgrades of the Source Engine since the release of Half-Life 2, for example, High Dynamic Range (HDR).

Half-Life 2: Episode Two
Half-Life 2: Episode Two is a first-person shooter released in 2007. It was the second expansion to the game Half-Life 2. Following the events of Half-Life 2: Episode One, Dr. Gordon Freeman and all the other major characters move into the wilderness away from City 17. The game uses the Source Engine.

Team Fortress series
The Team Fortress series is a series of first-person shooters originally developed by Team Fortress Software. Later Valve hired the developers so therefore the rights of the game were acquired by Valve. They remade the original Team Fortress using the GoldSrc Engine and titled Team Fortress Classic. Valve also made another Team Fortress game using the Source Engine and titled Team Fortress 2.

Team Fortress Classic
Team Fortress Classic is a multi-player first-person shooter released in 1999. It is essentially Team Fortress but running on the GoldSrc Engine with different character model, more maps etc. It also has different weapons, many of them were based on games in the DOOM series.

Team Fortress 2
Team Fortress 2 is a multi-player first-person shooter released in 2007. It is essentially Team Fortress Classic but made using the Source Engine with better graphicss, a new game mode, cosmetic items, etc. It was made free to play in 2011. Like the rest of the Team Fortress series, it has nine different classes the player can choose from.

Counter-Strike series
The Counter-Strike series is a series of first-person shooter originally developed by Minh Le and Jess Cliffe using the GoldSrc Engine as a mod for Half-Life. Valve then hired them both, and the rights to the game were acquired by Valve. Counter-Strike: Condition Zero was made using the GoldSrc Engine while Counter-Strike: Sourceand Counter-Strike: Global Offensive were made using the Source Engine.

Counter-Strike
Counter-Strike is a multi-player first-person shooter originally developed by Minh Le and Jess Cliffe as a mod for a game Half-Life (under the name Half-Life: Counter-Strike). Valve eventually offered them both a job; they agreed and the rights to the game were acquired by Valve. The game was officially released in 2000. The game uses the GoldSrc Engine.

Counter-Strike: Condition Zero
Counter-Strike: Condition Zero is a multi-player first-person shooter released in 2004. It is a follow-up to the game Counter-Strike. It features updated character models, textures, maps and other graphical tweaks. It also includes a singer-player campaign mode. The games uses the GoldSrc Engine.

Counter-Strike: Source
Counter-Strike: Source is a multi-player first-person shooter released in 2004 as a complete remake of the original Counter-Strike using the Source Engine. As with the original game, the player is put in a team of Counter-Terrorists or Terrorists, competing against the opposing side. The teams have to complete different objectives, depending on the mode is chosen, in a series of rounds.

Counter-Strike: Global Offensive
Counter-Strike: Global Offensive is a multi-player first-person shooter released in 2012. It is a follow-up to the game Counter-Strike: Source. It is essentially the same as previous Counter-Strike video games, with additional improvements and enhancements. It was also made available on the Xbox 360.

Ricochet
Ricochet is a multi-player first-person shooter released in 2000. It was made by Robin Walker, an employee at Valve, to demonstrate the potential of the Valve SDK. It is not as popular as some of other Valve's titles, however, it was still well-received. The game uses the GoldSrc Engine.

Deathmatch Classic
Deathmatch Classic is a multi-player first-person shooter released in 2001. It was mod for their popular game Half-Life; because Half-Life itself contains a deathmatch game mode, the mod did not get very popular. It is most of the time, the least played of Valve's release titles with only around 5 players every day (according to SteamDB).The game uses the GoldSrc Engine.

Day of Defeat series
The Day of Defeat series is a series of multi-player first-person shooter video games that originally started out as a Half-Life mod. It was not as popular as other Valve games but was still well-received. The game was known to be extremely hard as the player can die from just around three hits. The series uses the GoldSrc and the Source Engines with the two games, Day of Defeat and Day of Defeat: Source.

Day of Defeat
Day of Defeat is a multi-player first-person shooter released in 2003 originally started out as a Half-Life mod. Set in 1944 in the European theater of World War II on the western front. It does not include a campaign. The games uses the GoldSrc Engine.

Day of Defeat: Source
Day of Defeat: Source is a multi-player first-person shooter released in 2005 as a remake of the original Day of Defeat using the Source Engine. The gameplay was fairly similar to the original, however, the British army and several classes were removed, which resulted in reduced possibilities for gameplay.

Portal series
The Portal series is a series of first-person video games which were inspired by the game Narbacular Drop, which was developed by Nuclear Monkey Software. Valve hired the developers and made the game Portal. It was a huge success, and this lead to the development of Portal 2. Both games were made with the Source Engine.

Portal
Portal is a first-person shooter released in 2007. It contained no multi-player mode, only including a single player campaign. The game is most famous for the Aperture Science Handheld Portal Device (Portal Gun) which is a device that shoots portals. The game contains lots of puzzles that the player most complete. The games uses the Source Engine.

Portal 2
Portal 2 is a first-person shooter released in 2011, and was the sequel to the game Portal. It includes new features and contains a longer storyline than Portal. It is set a hundreds of years after the events of Portal. The game uses the Source Engine.

Left 4 Dead series
The Left 4 Dead series is a series of multi-player first-person shooters developed by Valve and Turtle Rock Studios. It is about four survivors caught in a zombie apocalypse. The first game were released on 2008 and just one year later, the second game was released.

Left 4 Dead
Left 4 Dead is a co-operative first-person shooter developed by Turtle Rock Studios and published by Valve. The game pits four survivors against a horde of infected. Left 4 Dead was well received, and Left 4 Dead 2 was developed a year later.

Left 4 Dead 2
Left 4 Dead 2 is a co-operative first-person shooter developed by Turtle Rock Studios and published by Valve. The game is essentially the same as Left 4 Dead but with more weapons, maps, and enemies.

Dota 2
Dota 2 is a multiplayer online battle arena (MOBA) developed by ''Valve. It is a stand-alone sequel to Dota which was a community made mod for Warcraft III'' developed by Blizzard Entertainment.

Extras
The following games were not official releases in the series and were either released on other platforms or meant to serve as technical demonstrations.

Half-Life: Decay
Half-Life: Decay is a first-person shooter developed with help by Gearbox Software and released in 2001. It is available exclusively on PlayStation 2. It is set in the same time as Half-Life but with the perspective of two female characters. The game uses the GoldSrc Engine.

Half-Life: Source
Half-Life: Source is an engine port of the popular game Half-Life using the Source Engine. It was released in 2004 at the same time as the Source Engine upon which it is based was also released. It was not very popular because of how badly ported the game is with only around 80 players every day (according to Steam Database).

Half-Life Deathmatch: Source
Half-Life Deathmatch: Source is an engine port of a portion of the popular game Half-Life using the Source Engine, released in 2005. It was once again. not very popular because of how badly ported the game was with only around 20 players every day (according to Steam Database).

Half-Life 2: Lost Coast
Half-Life 2: Lost Coast is a promotional tech demo released in 2005. It was originally created as a chapter for Half-Life 2 but was later cut; the developers turned it into a promotional tech demo demonstrating the new High Dynamic Range (HDR) lighting added to the Source Engine.