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
Quip - Quip is the modern productivity suite that simplifies your life and helps your team get work done faster.
Afloat - Create beautiful invoices in 3 clicks, without mistakes
VoltSim - VoltSim is an interactive realtime circuit simulator. It has digital and analog components and even Integrated Circuits. It is the perfect companion to students, hobbyists, and engineers.