Interlocked is a free Flash game, and a new take on a very old idea: mechanical puzzles. In Interlocked, you are presented with a three-dimensional shape composed of several interlocking parts (hence the name). You need to take the shape apart, piece by piece, by sliding the pieces around in the correct sequence.
The puzzle floats in the center of the screen. You can click and drag anywhere with your mouse to rotate it in any direction, but you can't zoom in or out. It just about fills the screen, but I found myself wishing for a zoom feature that would let me take a closer look at how two parts interlock.
Once you get the puzzle in position and want to try shifting a piece or pulling it out, press and hold the Space key. Now click a piece and a six-sided arrow will appear, one arrow for each axis you can move the piece in. To move the shape, just drag it in the direction of one of the axes. More often than not, you will bump against some other shape and need to stop. That doesn't mean you've made a mistake: You often need to solve a puzzle gradually, by shifting first one piece, then another, until you can finally pry one loose.
Sometimes Interlocked can get pretty frustrating. You can spin the puzzle around and around, push, pull and prod all sorts of pieces in every conceivable direction, and it still seems like it's all glued together. When that happens, you can try clicking the "hint" button, but don't expect too much: It would be something like "After removing the white block, play around with the yellow pieces." Not exactly a huge spoiler, but not very helpful either. If you really get stuck, you can always look at the official video walkthrough to see how each level can be solved.
If you don't find the normal gameplay challenging enough, you can try Interlocked's "Challenge" mode, in which the game measures how much time and how many moves you take to solve each level, and then gives you a star rating (1-5 stars). A wee bit stressful, at least for me.
The only minor nitpick I had with the game's interface is that to mute the sound, you must go back to the game's home screen: There is no way to mute from within the current level. Despite this minor flaw, Interlocked is a compelling game, and even made me want to get a "real" puzzle made of wooden blocks.
Note: The Download button takes you to the vendor's site, where you can play the game in your Flash-enabled browser.