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.
Circuito.io - Instant code and wiring for your project
Diode - diode - Android app to interact with reddit.
library.io - Learn electronics and easily create circuit boards online
Circuit Stickers - Peel-and-stick electronics for crafting circuits.
B4R - Development tool for native Arduino programs.