You're right. We were looking for an internal chat solution for our company. Currently we use IRC, but it would be nice to have an offline mechanism so we don't need to run IRC bouncers or CLI clients on our servers to receive messages when we're not in the office. We considered Slack, but decided it was too risky to host our internal communications on someone else's service. I'm waiting for the day Slack has a huge data breach.
We're currently considering adding some sort of backscroll support to IRC (maybe automatically setting up proxies for users), or installing Rocket Chat or HipChat on a local server.