There's a bunch of these things that date back to the late 60s. Became popular in the mid-70s and added sophistication as electronics improved.
In fact, you're simply paying for sophistication.
Every old "home organ" out there has something like this built in. I recently saw a Kimball organ on CL for $50 or so. It had a fairly involved auto-accompaniment panel. $50, a saw, and soldering.
Naturally, later units were tailored to more specific needs including one-man-band shows. The "Guitorgan" was a rig that actually wired the frets and connected with a huge 50 conductor cable to the guitar. The performer played guitar; played bass peds; and sang while the Guitorgan filled in strings, organ, brass, and all kinds of other layers with drums of every stripe. That was over 30 years ago.
Search for things like "auto-accompaniment" or "rhythm computer" maybe.
In short, what you ask is WAY too generalized. This stuff numbers in the hundreds over the course of longer than your lifetime.
On the good side, you got plenty to choose from. On the bad side, there's gonna be a little more homework involved.
Ponder5