any brain stretching games out there?

besides chess and portal? I really want to strech myself... recommend me anything worth playing.. thanksany brain stretching games out there?
Try World of Goo.any brain stretching games out there?
A mod for UT 2, Prometheus.EDIT: 3, UT 3, o_0 I don't know why I wrote 2.
yep I already finished wog, will check that mod... are there any particular specially for brain games I mean like those konzole japanese things which metr your intelligence.. I played something on psp which was called practical intelligence or something and it was based on solving problems and such... ?!
btw I will go for anything from puzzle to board games...
Braidfairly new game , very highly praised and for good reason.It's a platformer which introduced new concepts and innovative puzzles.Definitely try it , I just finished it and thoroughly enjoyed it.
You need to play Braid. It's a very emotional game and deep game.
[QUOTE=''PCGamer248'']You need to play Braid. It's a very emotional game and deep game. [/QUOTE]

I didn't start this topic, but I'm going to say thank you anyways, that game sound interesting I haven't got to enjoy it yet personally. Most the best ones have already been mentioned.
Zatikon for sure, people say it involves to much strategy lol. I like it though, sometimes it can get frustrating with all the things that can happen but I think that is what makes it fun tbh. But yeah, if you love chess you will love it.
You could try some of the harder adventure games, like Riven and The Neverhood
One word CrayonPhysics
the steam epic game: ''the path''and the myst game franchise is also good for this.