Virtual MIDI Piano Keyboard is a MIDI event generator and receiver. It doesn't produce any sound by itself, but can be used to drive a MIDI synthesizer (either hardware or software, internal or external). You can use the computer's keyboard or mouse to play MIDI notes. You can use the Virtual MIDI Piano Keyboard to display the played MIDI notes from another instrument or MIDI file player.
Khronosphere is an audio recording tool. Its special feature is a buffer that keeps capturing audio even before the actual recording is started. This enables the user to prospectively catch any interesting sound that normally would have been lost. The buffer size is freely definable by the user. The software itself places no restrictions; the only limits are the resources of the host system. Khronosphere is very similar to and inspired by Jack Time Machine. They both have the same basic concept, but Khronosphere supports larger buffer sizes.