MultiMC

MultiMC is a software application that enables players to create multiple instances of Minecraft, each with their own unique settings. While this application shares some functionality with the Minecraft Launcher, it has some important distinctions.

MultiMC offers the ability to download and automatically install Minecraft Forge, as well as LiteLoader. Because each instance is self-contained, the player does not need to spend time moving mods and config files around. The player is able to select from any version of Minecraft, going as far back as early Alpha builds (earliest available build reports itself as rd-132211; four classic versions, an infdev version, and multiple alpha and beta versions are available, as are all stable and testing 1.0 and later releases). MultiMC also has support for Feed the Beast packs.

Each instance has its own resource pack settings, and allows individual settings to be adjusted relating to Java, including custom Java binary, minimum and maximum memory allocations, PermGen size, and custom command-line arguments when launching.