Up here in Portsmouth NH, Tom has been running a session for at least a couple decades now & it a mix & it mixes well. It's generally folk. Traditional, contemporary, Sea stull, English, American, Scottish, Irish, singing & instrumentals, maybe some old country & even less a once & a great while bluegrass. It's pretty much all excepted as long as it's folk & it works extremely well. Everybody gets to sing a few & loads of stuff to join in on, you can just jump in or ask or if your seen singing along you'll most likely be asked to do something. It usually starts 4:30-to 5:00pm & lasts untill 9:00pm. It's probably the only mixer that I know of that works.
Good Luck
Barry