EventHorizon is a dot and debuff tracker and rotation helper written for WOTLK, Tuwz asked me to backport it so here it is! I don't personally use this addon, so if you run into any issues, make a ticket and I will investigate!
Original page can be found here: https://www.wowinterface.com/downloads/info11935-EventHorizon.html
Go to Releases in https://github.com/nullfoxh/EventHorizon/releases and download EventHorizon.zip. Extract it to your World of Warcraft/Interface/AddOns folder and you're done! Once you're done the path should look like World of Warcraft/Interface/AddOns/EventHorizon/EventHorizon.toc.