4four.io - Rhythm training exercises.
Virtual Piano - Free Online Piano App
EarMaster - Professional software for ear training and practical music theory on Windows and Mac.
VirtualPiano.eu - VirtualPiano.eu is a web-based tool that provides you the virtual Piano to play songs, learn the piano tunes, and create soothing song compositions.
musictheory.net - Music theory exercises.
Musicca Piano - Musicca Piano is the tool that allows you to play the virtual Piano from your computer.