Cubelue is a simple game, developed by some college student. It is completely free of charge and ads! You are a cube, that is trying to avoid some obstacles. That's it, how hard could it be?!
You play Cubelue by touching the right or left-hand sides of the screen. You get to the endless mode after completing a short tutorial. Beware, the learning curve is high!
You can unlock content like different player colours (600), different obstacle colours (1400) and a dark mode (2400) -for the most extreme- only by playing and reaching the required score.
As a gamer myself, I don't enjoy asking people for money for content and definitely showing ads while in the middle of a fun session. Everything is unlockable while playing. The difficulty is the same for everyone and only thing varying is the amount of joy.
Good Luck and Have Fun!