Here's as comprehensive a guide as I can come up with of commands that you're allowed to use. Commands are in bold; text displayed, if any, is after the "=>" sign.
/help displays all the possible commands. Many of them are useless, or you won't have permission to use if you're not a chat mod.
/me does something=> * InkL0sed does something
/notice something=> * something (InkL0sed)
/ignore username ignores user with name "username"
/unignore username unignores user with name "username"
/clear clears all the text in the room. This is good in conjunction with /ignore if there's a particularly bad spammer in the room.
/join Room joins Room if not already in the room. If you are, then it switches to that tab, and it doesn't display the below text. If the room doesn't exist, it creates the room.
=> * InkL0sed joins Room
/leave leaves the current room
=> * InkL0sed quit
/leave ch Room leaves Room
=> * InkL0sed quit
/leave ch Room "reason"=> * InkL0sed quit (reason)
/leave pv username leaves a private chat
=> * InkL0sed quit
/leave pv username "timeout"=> * InkL0sed quit (timeout)
/invite username invites user with name "username" to the current room
=> * username was invited by InkL0sed
/invite username Room invites user with name "username" to Room
=> * username was invited by InkL0sed
/privmsg username starts a private message with user "username". The only difference between doing this and creating a room and then inviting the person, is that nobody else can ever join the private message, even if you try to use /invite.
/send text simply submits "text"
=> <InkL0sed> text
/send /join also simply sends "/join". However, this allows you to type /join without calling the command and without a space before it, which is really the only reason why you'd ever use this command.
=> <InkL0sed> /join
/init disconnects from chat altogether, and leaves every room as well.
/quit does the same thing as /init, except it doesn't give you the message below that says "You must be connected to send a message."
/connect reconnects to chat. Obviously, this only works if the window is still open. Also, for me anyway, I only get plain text after doing this. I have to actually reload chat to get bolds, italics, colors, etc.
/version will give you the current version of Chat.
/whois username gives the true name of username. This will always return "username", since you can't actually change your "nickname", as Chat calls it.
/who does nothing. Well, ok, it gives you an orange bar below the text window. Yay.
/identify also does nothing. It only says "Identification failure"
Other notes:
When giving any argument after a certain command, if that argument has a space in it, you have to surround it by quotes. For example, if you try to do
/invite InkL0sed Second Social, you'll get an error. You should do
/invite InkL0sed "Second Social" instead.
Typing the up-arrow on your keyboard will give you the last message you submitted. Typing it again, will give you the second-to-last, ad infinitum. To go back down, use the down-arrow keyboard. Unfortunately, typing the down-arrow first will not give you your future messages. This feature cannot yet foretell the future.
Typing a person's name perfectly will bold their name, but only for them. So, this is how Chat may look to me:
<random person> InkL0sed
<InkL0sed> that's my name, don't wear it out
but to random person, it would look like this:
<random person> InkL0sed
<InkL0sed> that's my name, don't wear it out
Incidentally, clicking on someone's name will automatically add "someone's name, " to the text which you are typing.