Helium - Helium lets you accept payments by credit card for anything you want to sell online.
PiP for Mac - Always on top window preview similar to the popular windows only OnTopReplica
PiPer - A DIY Minecraft computer to build gadgets
CThruView Transparent Image Viewer - CThruView is a free transparent image viewer that allows mouse clicks to go through the image.
Pennywise - Cross-platform application to open any website or media in a floating window
Afloat - Create beautiful invoices in 3 clicks, without mistakes