Chat solves three problems for a conlanger: corpus building, proving your language design in a conversational context and tutoring the community. Most any chat tool works for the latter two issues. For corpus building, you really need to need to be careful what you pick because not all chat services do an equally good job of saving chat logs.
And by chat log, I mean the log of everything that has ever been said. Almost all chat technologies allow for saving the a single conversation, should a participant remember to do so.
This free, allows for self hosting and chat logs!
The chats are written to the file system, so there is always an easy to extract log.
Requires an open browser, as opposed to a IM client.
Requires some minimal skill in setting up a php website.
Lots of clients and a large community of people who know how to use it.
Lots of people don’t know how to use IRC.
Can be used from a browser, but doesn’t have to be.
Difficult to self host.
You can get free hosting at some websites.
No comprehensive chat logs unless you can get a chat bot to run, which isn’t trivially easy and the chat bot has to be hosted somewhere. Plus chat bots are also used for good & evil, so you will have to make sure over time your log collecting chat bot isn’t blocked for looking like a spam bot.
Sometimes chat rooms are logged by chat search engines
Sometimes chat rooms are logged by people who like your topic.
Other Web Based Chat Clients
Meebo and many other online chat services exist, often using flash or Ajax browser based clients. They exist, but I’m not going to write about them because logging is the sine qua non of a chat server for a conlang and many of these alternatives don’t have logs in the sense of a log of everything that was ever said in a chat room. Or if they do, they don’t let people get at it.