A new version of Jacker is out:
http://bitbucket.org/paniq/jacker
Changes:
* Command-Line support. If a song name is passed to Jacker at startup,
it will load it.
* "install" command. You can now install Jacker globally.
* New logo. Less glossy, more elegant.
* Fixed a terrible timing error that introduced a jitter as big as the
current latency.
* Default number of tracks raised from 8 to 16.
* Tracks can be renamed. Double-click track to pick a new name.
* Mute buttons for each track. Not that reliable at the moment. Last
played sound may hang. In this case, stop, then continue playing.
* MIDI input to connect your keyboard, to test sounds before you track
them. Click on a track label to route your keyboard to the particular
output.
* Initial JACK transport support. It's useful for synchronizing a
recording to a DAW like Ardour. Can be switched on with the "Sync"
button in the toolbar. Not too stable on start-up and loop borders.
When in trouble, stop, seek, then start.