Multi Minecraft Manager allows you to have and manage multiple instances of Minecraft, each with a different configuration and set of mods.

Yes, but as far as I know they are either Windows only, use custom launchers or require other complex set up. MMM works right out of the box and uses the normal Minecraft launcher.

• Manage an unlimited amount of different Minecraft instances.
• Works on all operating systems (Windows, Mac OS X, Linux).
• Launch the default Minecraft instance from MMM as well.
• No extra setup required (No Java in PATH, no Mono, no runtimes) ^[1]
• Stores instances in a known, convenient location (%APPDATA/.mmm on Windows, ~/Library/Application Data/MMM on Mac, ~/.mmm on Linux)
• Icon based view with option for custom icons.
• Uses the official launcher, or any launcher you want, including SpoutCraft!

Windows [.exe installer] [.zip file]

Mac OS X [.dmg image]

Linux Currently we do not provide binary builds for Linux, please compile from source (requires Qt and CMake).

Source Code MMM is zlib/libpng licenced, you can get the source code on GitHub.

[1] Technically not yet true on Linux.