Allthough this one is already listed in the Black Friday list, I thought it worth mentioning seperately especially for us Oxygen users.
Sometimes Oxygen can be a bit tricky when updating and keeping your site running (I have never experienced issues myself but I read about others having issues) and that's where WP Reset comes into play.
It keeps a snapshot of your database (automatically if you wish) of everything before you do any update. It does more but I think this is the best part.
There is a great deal on AppSUMO worth buying.