Another key difference:
Chat is largely expected to be real time where replies are short and might occur in a few minutes. The text content is ephemeral, which means it doesn't endure.
On message boards, or forums, the replies are generally longer, but so are response times, which can take hours or sometimes days. Also, most message boards are publicly viewable by anyone, even anonymous users who aren't logged in (so keep this is mind before sharing any personal information). However, the text is expected to endure for an indefinite period of time. It could be months or even years.
1 day