JJazzLab is widely considered the best free, open-source alternative to Band-in-a-Box (BIAB). It is built specifically for musicians who need automated backing tracks based on chord progressions, but want to avoid the high price tag and cluttered interface of BIAB.
Below is a detailed breakdown of how they compare, their strengths, weaknesses, and what you need to know about setting up JJazzLab. Feature Comparison
Band in a Box Alternative JJazzLab (FREE Software) – Installation and Overview