Epic Pen - A windows tool for drawing over your desktop and applications
PiP for Mac - Always on top window preview similar to the popular windows only OnTopReplica
gInk - An on-screen on-screen annotation software for Windows.
PiPer - A DIY Minecraft computer to build gadgets
Gromit-MPX - Create annotations by directly drawing on your screen.
Afloat - Create beautiful invoices in 3 clicks, without mistakes