Check out this experimental touchscreen DJ mixing desk interface designed by Gregory Kaufman. It's stunningly crafted, if potentially a little unintuitive for mass market. The various 1, 2 and 3 finger gesture combos might make it tricky to remember what does what. All the same, it's great to see things moving away from the traditional turntable / CDJ's and into multi-touch interactive platforms.
MuBlip is a nice progression in the sequencing game genre. Users need to remember light patterns and gestures in order to successully play back the musical sequence in time. The 8 Bit electronica sound track is pretty good too.
It has been created by Para9 in Montréal
MJUVI
Here's another great audio visual sequencer, but this time generated by motion tracked people. The user chooser can choose different modes which get assigned to them, by connecting with other people nearby the musical score gets arranged by a sequence of triggered midi signals. The project was developed using Processing and C++. Mjuvi is a 2010 student project at h-da
Inkquencer
Inkquencer is a simple concept created by Sebastian Thielke whereby users hand-draw squares on paper and interpret them into a music sequencer by real-time recording through a computers camera.