MultiMC 5 - Mac OS X (x64)

MultiMC is a free, open source launcher for Minecraft, managed by Forkk13, peterixxx and drayshak. It allows you to have multiple, separate instances of Minecraft (each with their own mods, texture packs, saves, etc) and helps you manage them and their associated options with a simple interface.

Official site: multimc.org

Features

• Manage multiple instances of Minecraft at once
  
• Start Minecraft with a custom resolution
  
• Change Java's runtime options (including memory options)
  
• Shows Minecraft's console output in a colour coded window
  
• Kill Minecraft easily if it crashes / freezes
  
• Custom icons and groups for instances
  
• Forge integration (automatic installation, version downloads, mod management)
  
• LWJGL version changing built-in
  
• Supports every version of Minecraft that the vanilla launcher does
  

To install:
Extract the archive to a new folder and run it.