is a "macros-cache.txt" storage tool for World of Warcraft. Let me explain it: WoW stores all macros from your account to the "macros-cache.txt" in your WTF/Account/accountname/ folder. Each account has 36 macro slots. If you relog or /reload your UI the current ingame macros are saved to the Blizzard servers and the macro-cache.txt on your computer.
Arena / PvP player in example often need more than 36 macro slots for one character. With iSlot you are able to store unlimited macros and activate them with just one click and type /reload or relog your character in WoW.