Gmorgan Play Along
I subscribe to a free service: Jazz on the Tube that sends a clip about every day. Here's an example: http://www.jazzonthetube.com/videos/count-basie/slow-blues.html
With that inspiration:
GMorgan is a free program which you can download from Sourceforge. It works well for me using Ubuntu and a Yamaha Motif ES8 keyboard. Probably it runs on other Linux distributions, although Fedora could not keep time...(I didn't install the correct graphic driver for Nvidia.)
You don't have to install GMorgan though. Try playing along with this slow blues in Bb, a YouTube video which is screenscraped from GMorgan0.58. Get your instrument and open full screen. (If the Youtube isn't clear enough drop me a note and I'll send you a link to the original file.)
I couldn't resist adding some illustrative accompaniment tracks. Watch on the left of the screen for pattern changes.