I got this from the Groovestep Google Group:
This is just a notice that the group will be shutting down soon. It hasn’t had much activity lately and with the great amount of audio apps on for the iPhone OS, the DS platform for homebrew music app development has been made obsolete.
Thanks for all the support and may Darwin bless you!
Sad really, but I think that many platforms will be experiencing similar problems at the expense of the iPhone OS and soon the iPad too.
Sad day for the DS nonetheless.