PiP for Mac - Always on top window preview similar to the popular windows only OnTopReplica
Circuito.io - Instant code and wiring for your project
Pennywise - Cross-platform application to open any website or media in a floating window
library.io - Learn electronics and easily create circuit boards online
Afloat - Create beautiful invoices in 3 clicks, without mistakes
B4R - Development tool for native Arduino programs.