...do a search for "emacs foot pedals" and you'll find many results. Years ago when I got my first Mac I had visions of buying all these cool MIDI devices and trying to control it with those. As an 11-year-old without internet access I hit a dead end pretty quick, but there are certainly others with the idea.[1]
[1] http://stackoverflow.com/questions/5928061/using-a-piano-key...
One thought, since the Teensy can detect button press and button release events, is to code a vim mode where holding the pedal puts you in insert mode and releasing the pedal hits ESC to leave insert mode. We'll see how that works out in practice.
For 3 pedals, you could go with a DIY guitar pedal solution of project boxes and 3 momentary stomp switches (http://www.mammothelectronics.com/ is a good supplier of these parts) but I am unsure about the ergonomics of using one of these pedals constantly. (Guitarists simply stomp them on and off from a standing position. They're generally not pressing and holding the switches for 8 hours from a chair. So it might just cause foot/ankle problems due to the height of the front of the enclosure. More experimentation is needed on my part in this area.) Such a pedal would be way cheaper than the commercial versions from Kinesis and other manufacturers, however, and should be far more configurable / useful on Linux & Mac.
http://www.kinesis-ergo.com/fs-savant-elite.htm http://www.kinesis-ergo.com/fs-elite-single-compatibility.ht...