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 (or s): when is that State of the Union address due?
random (or r): 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 (or u): forget that cover sheet?
tag: is this for work or for fun?
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?
reject: ... or leave them hanging?
delete: accidentally created a task you don't want?
history: who did what when now?
Working with Hiveminder by IM:
feedback: want to tell us something?
privacy: need to see our privacy policy again?
You can also use 'help command' to receive detailed help on a specific command.