For Super Happy Dev House SG, I hacked together a little mailing list manager which has no setup, you just email {something}@lists.haller.ws, and if that list doesn't exist, you get control of it, and any people you cc on emails to the list are automatically added.

Likewise, anyone who replies-all with the list address and cc's someone new, that new person also is automatically added. Which means we don't have to keep track of annoying CC lists and making sure that everyone was cc'd who needed to be. And no one can post unless they've been cc'd in (so no spam ;).

For small ad-hoc working-groups, this just rocks. I helped build the SHDH wireless setup ( 1 cisco air, 1 airport extreme, 3 colubris MAP-320s) to support 100+ people, their laptops and their phones. By the end of the two weeks, the cc lists had gotten out of hand, and between the coordinators, we had all dropped some balls (luckily nothing network perf affecting).