I have two different friends who hold jam/parties about once a month or so on Saturday nights. They schedule them so they don't conflict with each other as many of teh same musicians go to both jams. In fact, I just went to one this past weekend and it was a blast.
These aren't very formal though. No song lists or anything. We usually have a few guitarists, a few bassists, at least two drummers and a keyboardist or two. We just trade off playing and jam whatever anyone starts playing. It could be a cover, or just a chord progression someone likes. This makes for very unique jams everytime we all get together.
I should mention pretty much everyone involved in these are very longtime players. Most are around my age (Mid-40's) and have been playing their instrument for 20-30 years now. Have been in and out of bands together and for many of us, knew each other before anyone had ever even picked up an instrument, so our dynamic is a bit different than yours probably is.
Most of us gigged for many years and just aren't as interested in putting in the time required for a steady gigging band, so we just play out once in a while and jam frequently at these jam/parties to get our live playing jones out of the way. lol...
Best of luck with your idea. Hope it works as well for you as it does for the guys I play with.
