One of the best things to have ever been created for an Android device (whether tablet or smartphone), and despite the fact that its on a mobile platform you'll find that it pretty much turns your Android device into a fully fledged touchscreen based electronic music making DAW.

As veteran electronic sound makers of the android version will know, USB midi control for some of the most popular midi keyboards is built in, making it even easier to use beyond the touchscreen interface.

Well it looks like Windows surface and Windows tablet users in general haven't been left out of the touchscreen based processor resource sipping Caustic mobile DAW electronic music making antics either, as there's now a free Windows version direct from the Caustic website. The only stated caveat is that there is no technical support for it like there is for the Android and Playbook version (if you bought it).  Aside from that you'll find that all external midi USB controller features are included and all in tact.  Unfortunately though there still aren't any external midi clock sync features. 

True fully featured touchscreen interface based music production right now? (and not a half assed yet to come flowing futuristic concept destined for high premium user only use through specialised manufactured hardware implementation eg. The Jazz mutant). Who knows where it could go if it gains further traction and wide spread support. But yeah, its currently free for metro GUI tablet users. Hopefully it will stay processor light and incredibly fast as it is now with any future leaps that might be made for it, no doubt the fact that its original development for fast and smooth running on the Android platform has a lot to do with that.

Additionally you don't actually need a touchscreen or variants of windows 8 to be able to use it on a windows laptop (and external USB midi keyboard features are still fully functional), but it does make it a damn sight easier than point 'n' click if you have a touchscreen with windows 8 touchscreen interactions. You can get it here.