In case you got some time to kill, or simply prefer to 'productively' kill your office hours, than here you go: five very popular, mind-challenging and fairly addictive games on the web.

(1) Desktop Tower Defence - highly addictive, challenging and very popular puzzle/strategy game where you have to protect your desktop from creeps (invaders) by building a labyrinth-like maze along with firing towers on the walls. Finding the right places for the firing towers is the main key here.

(2) Bloxorz - not as fast-paced and intense as Desktop but no less challenging, accompanied by excellent graphics and sounds. The aim here is to get the brick-like block to fall into the square hole at the end of each maze. There are 33 stage to complete.

(3) WebSudoku - thousands of web-based classic Sudoku puzzles for any level from beginner to expert.

(4) kdice - live turn-based multi-player strategy game. The goal of the game is to conquer all of the territories owned by other users. Read more on Kdice on Wikipedia.

(5) CDX - realistic flash-based mystery game. The main character Adam (you) is suffering from amnesia. You have to solve various tasks to get to the next task. Tasks range from deciphering codes, withstanding interrogation, to solving mazes in Rome. 4 level game.

(6) Additional Stuff

  • Good Experience Games [goodexperience.com] - "... good game design with an overall attention to quality. Unless otherwise noted, they're all free, online, and available right now."