You can train cats with Clickers there is a thread here where someone was talking about how their training was going and some other members use this also. It's mostly basic commands, roll over, kiss, shake, stay, sit, lie down, etc.
I think cat IQ and willingness really depend on the cat. My last cat did nothing but keep you company and fetch. Oh and she asked permission before jumping on things ~mew~ pause ~MEOW~ jump
My Kilala fetches, tries to open doors but he has furry paw pads so he slips, he will open closets (sliding doors) for no reason just attention, he talks back to everyone as if normal conversation, insitgates chases and can turn off switch lights ( finally trained him with the laser pointer)