game recommendation – What online collaborative communication tools have the most components for roleplaying away from the table?

I run a lunchtime game session once a week. Due to temporal constraints, we try to keep our sessions around the table limited to the more active aspects of encounters; for example, those that require maps, charts, spreadsheets, figurines and/or copious amounts of dice rolling. As such, we move much of the actual roleplaying away from the table and onto alternative forms of collaborative communication.

Until recently, the method of choice for these interactions was Google Wave. However, with its impending death, we now find ourselves without an adequate communication tool for PC/NPC interactions (i.e. plot development).

What now is being lauded as the best communication tool for RPGs and what are the compelling features? I’m looking for web-based options more specifically, since my players use differing OSes and the web is a universal platform.