In my area there is a musical get-together every weekend as well as several others during the week...each one has a bit different focus.

1st sat. open folk jam
2nd sat. open music circle
3rd sat. old time music jam
4th sat. bluegrass jam

and there are harp circles, rise up singing circles, blues, etc.

we post the schedules of some of these on our calendar
www.bfms.freeservers.com on the Folk Society Website.

also some are listed on www.folkjam.org
here is their national map..unknown if they have international
listings....http://www.folkjam.org/national/map

here are some other mudcat discussions on this:

singaround, jam song circle or session - 1999
http://www.mudcat.org/thread.cfm?threadid=12109#93528

slow jams - 2003
http://www.mudcat.org/thread.cfm?threadid=56162#877232

song circle locations 1997 - 2006
http://www.mudcat.org/thread.cfm?threadid=2312#1687233

elite jam session etiquette
http://www.mudcat.org/thread.cfm?threadid=13463#110822

song circle or jam 2003
http://www.mudcat.org/thread.cfm?threadid=58832#933127

open jam sessions 1997 - 2000
http://www.mudcat.org/thread.cfm?threadid=2799#12275

i saw one of these threads described as a retired perma-thread
can we bring it back out of retirement?