Here are the commands I know about:
Creating tasks:
create (or c): got more stuff to do?
Finding tasks:
todo (or t): what needs to be done?
search: when is that State of the Union address due?
random: feel like letting dice plan your afternoon?
review: need to look at every task?
show: what tasks am I playing with?
Working with tasks:
done (or d): been there, done that?
undone: forget that cover sheet?
tag: is this for work or for fun?
untag: got a little too tag-happy?
tags: need to know which synonym of "awesome" you used?
comment: task needs some fleshing out?
due: when do I need that 1000 gallons of water?
hide: need to wait until next week for this one?
priority: need to impose some order on your tasks?
give: want to suggest that someone else does this?
accept: want to help your friends/coworkers/boss out?
decline: ... or leave them hanging?
delete: accidentally created a task you don't want?
history: who did what when now?
then: #A then #B?
rename: has your task changed?
move: want to let the SPECTRE group in on your world domination plans?
note: would you like to know more?
unowned: are you the one who deals with writing help files?
Working with Hiveminder by IM:
feedback: want to tell us something?
privacy: need to see our privacy policy again?
alias: tired of repeating yourself a lot?
filter: got a case of tunnel vision?
date: what year is this, anyway?
url: need to see tasks in your web browser?
unlink: need to switch Hiveminder accounts?
whoami: too many accounts to remember?
invite: want to spread the buzz?
You can also use 'help command' to receive detailed help on a specific command.