- All content invisible to outsiders.
- Anyone with a "@mygroup.com" email can join my group.
- Channels can be visible to whole group, or invite-only.
- For each message, see sender and time.
- Channel notifications can be configured (eg. mute this channel)
- Keyword-matching notifications that override channel settings.
- Threaded discussion
- Text visible to all while typing.
- Several users can edit the same message at the same time (like in co-meeting and Google Docs)
- Jump to next unread message by pressing space or similar. Jumps to next channel when all messages are read in current channel.
- Messages can be edited after sending, but are marked with time of last modification.
- Desktop/laptop-oriented web site.
Less important requirements:
- Android app and iOS app, or mobile website.
- Integration with Github/Bitbucket/Google Code (commits and issue tracker updates appear in a channel).
- For each message, easily like/dislike/mark as task. Such marks are visible by all.
- All features also work with Japanese names (unlike Slack).
- Ability to mute a particular thread.
Can cost money.