While no longer using an IRC backend, Slack offers a lot of IRC-like features, including persistent chat rooms (channels) organized by topic, private groups and direct messaging.[15] All content inside Slack is searchable, including files, conversations, and people. On the free plan, only the 10,000 most recent messages can be viewed and searched.[21] Users can add emoji buttons to their messages, which other users can then click on to express their reactions to messages.[22]