[yason]

IRC has always worked well. Done this in several companies. IRC is both real-time and offline. Even your toaster can run an IRC client so it's completely platform independent which is a big thing with engineers.

In a work environment people stay on global and per-team IRC channels. You can a) chat online if there are colleagues online and b) when you get back from your coding session you can always review what others have been talking about since yesterday. You can also chat in a relaxed way as in replying back every 10 minutes or whenever you don't have more important things to finish. This means you can extend your online presence over the workday with a latency of checking back several times an hour while still not getting bounced by each and every message someone decided to send you.