If you’re like me, your Android devices don’t stay stock for very long. Sometimes my devices are rooted and have alternate ROMs on them before I’ve even fired it up for the first time. Siyah Kernel is an alternative kernel for the Samsung Galaxy S3 (and S2) that allows you to adjust things like CPU speed, under- or overvolt CPU and GPU, and a myriad of other tweaks. It also allows you to setup a dual boot system.
Want to run stock Samsung Touchwiz because of the great camera app or the FM radio, but also love to run an AOSP ROM like Cyanogen? Want to muck around with alternative ROMs just to see what added functionality you can get, but want to be able to easily revert back to your old ROM? Siyah makes it easy to load and swap between ROMS (press volume up or down on boot ) and do things like easily swap the preferences of primary and secondary rom on initial boot. There’s full support on XDA-Developers, but be warned that if you get into alternate ROMs, it can be addictive.