[stupid comment]what exactly is CalcSys, an OS on top of an OS? I have no idea.[/stupid comment]
Looks awesome, though I have no idea what it is 
CalcSys is a flash application written for the Ti83+ that hasn't been updated in forever even though it could use some updating. It was basically zStarts partner as the ultimate swiss army knife app, though it came first. It could be described as "WikiTI in an app" for all the things you can learn about the calculator using it, but it's really just a Hex editor for memory on your calc. There is a flash editing version called CalcSysX but no binary of it has been built, it's source is online with BrandonW.
It allows for low level control of just about anything, and if you know the structure of the ASM code of a game well, you can use it to cheat. Axe is especially easy to cheat on

You can use it to set system flags to change how the OS works, and dissassemble programs on the fly to find certain instructions. In the final of THIS, I'm guessing, will be included the feature I'm about to describe for Calcsys:
A console. Epic, right?

It also has key-press info, font info, token info, and link port monitoring.
My very favorite, though, is hardware port modifying. You can pretty much use calcsys for ANYTHING.