I think IM is a bit of a misnomer when applied to products like Kato. Persistence, sync across devices, and instant search make it a lot more like "multi-person

I think IM is a bit of a misnomer when applied to products like Kato. Persistence, sync across devices, and instant search make it a lot more like "multi-person, temporally-organized Evernote, with real-time feedback", which is closer to replacing email than IM. For what it's worth, the Kato team so far hasn't sent a single internal email over the history of the company. (We're distributed across ~15 cities.)