Floating Point is an amazing relaxing game which can be played entirely using only the left and right mouse buttons.
The game has a very satisfying and fluid physics system and responsive controls. It's very easy to learn and master, but even inexperienced gamers will have no trouble playing the game, as there are no time limits, no restrictions, it's simply level after level with the only goal being to "collect" every "red bars" on the current level to move on to the next, which is pretty much the same thing over again.
The game is particularly relaxing and a nice "time waster". It's simple, fun, easy to pick up but hard to let go.
It's the kind of game you just launch and play for a few minutes while waiting or doing other tasks, or simply to relax and unwind for a bit. It features an excellent and equally relaxing soundtrack.
And finally, the strongest point for the game? It's absolutely free. No pay-to-win, no exclusive content, no DLCs, you just iniciate the very small download, launch the game, and enjoy it freely. To be honest, I consider this game better than most paid games on Steam. Turns out there are some hidden gems in the free-to-play section of Steam.
The only cons I can think of for this game is the fact that the gameplay can get rather repetitive; No real goal, not much challenge, and it most certainly won't give you much sense of achievement. After a while, just going level-to-level can get slightly boring.
Overall, I HIGHLY recommend this one. It's free, so you know you've got nothing to lose. Heck, I'd recommend it if it were a paid game either ways.