What is it? The GT-R1 combines a full featured flash recorder with something called a music trainer-- a device that lets you loop and time stretch musical passages so you can learn tricky licks. There are other tools like part cancel and a very good tuner in there, too.
The recorder features a very cool "sound-on-sound" feature where you can over dub new parts. It is optimized for guitar and bass, with both mics and a 1/4" input plus piles of FX.
Read the review to get more-- and to hear audio examples (no bagpipes this time, just my so-called vocal).
The bottom line? A very cool tool for any musician or songwriter.
I also have a Tascam CD trainer and it is a very useful tool. The combination of overdub recorder and MP3 trainer into one makes spending that kind of money on a pocket recorder a lot easier to justify.