We're not bound by any ideology or musical ability — just the desire to sing with others. Well, that, and the desire to eat pie.
More practically: You'll generally find between ten and twenty of us a given singing, and we really run the musical-ability gamut: from folks who were told to mouth the words in music class through those with advanced degrees in musicology.
Our singings are kid-friendly — an accompanying child often has one or more others to play with. It can be useful to inquire in advance if considering bringing kids, so others have an excuse to bring theirs, too.