Twitter-like setup would be great. Just make sure to NOT use Modules that distract from main focus - just use Updates in Timeline, not Posts or Discussions, Albums, etc. The key is in keeping it simple.
We work with different implementations, like local/regional networks separated into locality subgroups, professional networks for certain occupations, specific interest networks, some political causes, collaboration networks for niche markets, customer communities complimenting main business, venue patrons communities, etc.
Sorry if that’s a bit vague - we can not share actual ideas or links.