This is an amazing app. Not only does it emulate a Mackie Control Universal (MCU) but it also has various MIDI utility screens with configurable controls and a piano keyboard. A hidden feature, explained to me by the (responsive and helpful) author on his support site is that 2 MIDI connections may be established and "cross-configured" to allow it to function as a WIRELESS MIDI INTERFACE. Using a cheap PC USB/WIFI dongle, you can easily set up a wireless connection between, for example, a USB keyboard and laptop.
The recent addition of mnet wireless MIDI drivers for Windows (http://www.humatic.de/htools/mnet/download.php) makes the wireless MIDI setup much easier than it was using rtpMIDI.
Touchdaw is a great value, and a great app too. It's a Mackie controller on your Android device that connects to your DAW over WiFi (and even over USB and BlueTooth if you are an "advanced user"). Meaning you can e.g. sit at the piano and control your DAW, including faders, automation, transport, etc. It works over the same infrastructure as the remote iPad app for Logic X.
If you are running your DAW in Windows you have to first install Apple's Bonjour, Tobbias Erichsen's free rtpMIDI and configure stuff that isn't native, in addition to dealing with Wifi, Firewall and TCP/IP issues. It might or might not drive you mad. Once you get over the hump, it runs OK. TouchDaw itself runs just fine, it's just that on Windows the protocol stack is a bit fragile, so it's more appropriate to say it runs OK.
On a mac it's much much easier, and it runs very well. This is because OS X has Network MIDI well integrated. It's also much better at recovery from disconnects and other inevitables that on the Windows side can require restarting stuff.
If you are already running a hardware control surface, there are different ways to mate TouchDAW with it. In Logic it's relatively easy to run the two in parallel. In Cubase the tendency is to spread channels between control surfaces, so tracks 1-8 might be on your hardware faders, with 9-16 on TouchDAW, which is not exactly desirable.
This is a fantastic app for advanced users to add to their setup. There are great rewards to be had, but also lots of potential pitfalls. There is a free version of TouchDAW that can be downloaded to check how well you will manage to get it running. Definitely start there.