Tentrix

TenTrix is what happens when Tetris goes to the beach to relax. There aren't any blocks flying down the screen at top speed. Instead, you get a nice 10x10 square and a lot of time to think. All you have to do is put colored forms on the board so that the lines are clear. When you get home, you'll see that you filled the middle with junk, leaving no room for a big square.
In the game, you get three pieces at a time. You have to use all three before you can get a new set. TenTrix doesn't have a "down" button, so you can only clear rows by moving them up or down or left to right. Only when you look at a piece that won't fit do you lose. The game is over, so you don't know what went wrong after that.

Tips That Will Help You Stay Calm

Don't play Tetris here; think about it in two dimensions. You can begin building anywhere: in the middle, at the top, or at the bottom. Use the whole board.
Don't fear the 3x3 big square. It's the worst thing that can happen to a run. You should always leave a nice open place for the game to end.
Early Clear Lines: Don't try to make a big art piece. If you can, get rid of a line. The most important thing you have is space.
Don't Put Yourself In A Box: Don't leave any empty spots. A lot of the pieces are too big to fit in a one-block spot.
There are a lot of "L" forms, so pay attention to them. Figure out how to connect them so the board doesn't look like a rough mountain range.

Things That Are Important

The pieces stay where you put them when there is no pressure. No one will fall, turn, or be afraid.
Free-form play means that you can keep playing for as long as there is space. You can play this until the year 3000.
When you're on a three-piece set, you can always see what comes next. It helps you choose what to do next.
You can leave, get something to eat, and then come back because there is no timer. When you're ready, you can play.
While chasing the high score, it's very satisfying to see that number go up while your board stays clean.

You can play TenTrix for "just five more minutes" and it's great. It's easy, bright, and surprisingly fun to play after you start trying to beat your old score. You can take a short break from thinking or spend a long time trying to figure out how to beat a 10x10 grid. Don't forget that big square will get you in the end.