PiP for Mac - Always on top window preview similar to the popular windows only OnTopReplica
Helium - Helium lets you accept payments by credit card for anything you want to sell online.
Pennywise - Cross-platform application to open any website or media in a floating window
Product Hunt Shell - A geeky, web-based shell for browsing Product Hunt
Afloat - Create beautiful invoices in 3 clicks, without mistakes
Screen Commander - Blank your screens at the click of your mouse.