ExtremeLauncher is an unofficial Launcher for Minecraft, Extreme Launcher is a freeware released under the MIT license. It was meant to be a faster and lighter alternative to some of the slow launchers out there, offline-mode and online-mode are both supported, but you won't be able to use online-mode with an account that was already migrated, we're still working on a solution for that. All versions of Minecraft are supported, just be sure you have the right version of Java installed on your computer.