The people at SOURCEFORGE keep amazing us all with their generous concept of supplying quality software solutions to us for free: stuff that can easily rival the really expensive alternatives.
IMPRO-VISOR is one such program that can be a real help to the student of improvisation. My students and I use it to create backing tracks that we can solo to. Basically you type in your chord progression, choose a tempo and style (swing, latin, blues etc.), and away you go: piano, bass and drums give a convincing accompaniment for you to practice your soloing.
You can choose the type of bass, and change the piano to a guitar if you prefer; basically there’s plenty of fun things to explore if you’re so inclined.
Here’s the link:
You can use it with Windows or on your MAC. Read the instructions carefully though (Windows 7 gives a bit of a problem but you need to load it to your desktop): it all works when you know how. They also have a great Tutorial:
https://www.cs.hmc.edu/~keller/jazz/improvisor/ImproVisorTutorial4.htm and HELP Menu.