For me, Google Docs has been a stand-out winner for collaborative efforts. In some instances, it is for projects where team members are spread far and wide - from Adelaide to Malaysia and back again. For other times, it's the desk next door, but it's happening in the final hours of a deadline. Either way, Google Docs somehow makes this work.
Your ELGG (an open source community platform) users might not be overly concerned about their friend count, but they very often might need to make a connection with your organisation right off the bat if they have questions about how to use the site or need to understand what having a friend or contact entails so they have the confidence to start engaging with other users.
If you currently use or are considering implementing ELGG, you may want to think about starting your members off with at least one default friend.