PowerFX's Soundation Studio is a web-based DAW, and one that's been making steady progress since its launch in 2009.
In a significant development, Soundation Studio now supports external MIDI recording, meaning that you can plug in a controller keyboard and play the four synths, drum machine and sample player.
For many users, this will increase the creative potential of the software considerably: check out the Soundation website for a guide to setting up your MIDI keyboard, or proceed directly to the Soundation Studio launch page.
For more on online music making, check out our 9 ways to make music in your web browser.