Trebene seems kind of easy but is trickier than it appears. Your objective is to score points by grouping 3 or more similar colors in a group. New tiles slide in a la 2048 and/or Threes!
If the board fills up completely, game over. Here's what's interesting: if you empty the board completely, your game ends. Which means that playing perfectly will yield a low score.
Practically nobody is playing Trebene, even though it's free. There are maybe 15 players on the Leaderboard.
Trebene is definitely worth 20 minutes of your time.