Donno how many of you know abt this but it's one of the best time pass I've come across..
Created by some of IIM-I guys (Indian Institute of Management - Indore) it is simply-too-good..

Original KlueLess Part 1. Don't forget to read the rules without which you won't get anywhere.

Second version they released is KlueLess Part 2. Rules are similar but after doing part 1 you would surely be careful enough to read them. :)
The link to the game is inside the rules.

PS: You'll find many blogs with hints etc. But beware of spoiler blogs that have the answers.