Here is something very cool. SpliceMusic has created a free, online sequencer.
You simply upload your sounds and songs from your browser, then create songs with others amd mix them with an oline sequencer. You can collaborate and create songs together and anyone can remix them rrom any browser. It's easy, it's fun and it's easy and best of all it's free. The interface is intuitive and every track has volume, pan, mute and solo control.