Addictive, minimalistic, frustrating, brain-melting fun. If I could have just four adjectives and a noun to describe Hello Worlds!, I would pick those exact words. Get ready to meet one of the most engaging Flash platformers you can play in your browser, for free, right now.

Each Hello Worlds! level is split into two, three or four parallel worlds. A wall in one world will block your way in all worlds; a platform in one world will hold you aloft in the other ones. The whole game is built on the interaction between these worlds: Stand on a ledge in one world, and jump onto a higher ledge in another world.

Each world has a door; when you get to it and hit Space, that world disappears. Sometimes it goes away entirely, leaving you with a simpler level, and sometimes it is replaced with another world which you must now navigate. Every Hello Worlds! level also has a "level door," which you must reach to complete the whole level. Oh, and don't forget to collect the stars you see along the way: They help the score, and allow you to get to the more advanced levels.

Making it through a level depends on navigating all worlds correctly. If you trigger the door on one of the worlds too soon and make it disappear when you actually still needed it, you will not be able to complete the level. Fortunately, you can press and hold V on your keyboard to undo your actions. This isn't a quick undo to a save point, but actually a rewind much like the one in a VCR (or VLC, if you're more modern). You see your character quickly retracing its steps, and can release the V key at any time you want to stop, even midair.

Hello Worlds!'s rewind feature doesn't just retrace running and jumping, but all actions. So if you just realized you shouldn't have made that last world disappear, no problem--just rewind.

When a level is split into four, it can get tricky to visualize. Sometimes you see where you're trying to go, but you're not quite sure what you should be standing on to get there. When that happens, you can hit C to converge all parts of the level, so you're looking at the whole picture for once. But you can only look: While holding C, you are not allowed to move.

Hello Worlds! does away with many of the frustrations present in other games, such as constantly dying or having to run like mad. If you like to combine running and jumping with thinking, this free game deserves at least one coffee break.

Note: The Download button takes you to Kongregate, where you can play this game in your Flash-enabled Web browser.

--Erez Zukerman