Adium has had OTR out of the box for as long as I've known about it, and you don't have to do anything special to make it work; just talk to someone else that wants to do OTR, and it'll pop up at you.

(I use adium too...) I was confusing it with Pidgin for needing the OTR plugin. Adium (and Pidgin) have had security issues in the past due to libpurple; a lightweight app would solve that. I want something where you can just tell someone who starts talking recklessly on FB messenger or SMS or whatever to go to a single URL or download a single app and have pretty high confidence it will work.

Mobile is probably more important in the long run, especially for the kind of activist users CryptoCat seems to target.

(Another obvious thing is just i18n/l10n for arabic/pashto/etc., of existing tools.)

Another feature which would be nice is Grugqian "anti-forensics"; Adium for a while logged OTR chats by default, and even retaining OTR keys could be used against you (even if it doesn't allow decryption of past messages, it is enough outside of a court of law to link you to activity...). A browser extension or mobile app which didn't save local state (doing key derivation from a passphrase?) would probably be great for that. Add in SnapChat-style "no logging in the application", and honest-but-stupid counterparties wouldn't log chats.

The only weakness I see is no great way to do message-encryption for multiparty right now in a standard way. I'm not sure how you can do multiparty key agreement with PFS using anything outside academic papers.

It's hard to think of a well-regarded widely-used multiparty encryption system, which is a good reason generalists shouldn't try to implement them.

It's fairly straightforward (conceptually, if not in actual implementation) for a system without PFS, since you can reduce the problem to N interoperating conventional public key systems (e.g. how PGP works for multiple recipients). (and, obviously, just use OpenPGP for it...). But PFS is probably highly desirable in the "Syrian protest" scenario.

Or with a trusted third party (at the limit, just do irc-over-SSL.) This is probably fairly safe if you pick your TTP correctly -- I'd trust the NYT or USG even if I were a Syrian protester with the FSA.

I agree overall -- and am not trying to defend CryptoCat, just the CryptoCat market niche.

On mobile, there's something called Gibberbot for Android but it's XMPP-based and fairly fiddly to get working.