Bonk.io

A simple but elegant io game. You are a ball, and you want to knock other balls to the ground.

One thing I like is that rounds in small, 4 person lobbies, rather than the massive worlds of other io games. Although you can't really make friends, you can know personas, and it's more personable.

Code Romantic

Learn the pleasures of loving another human, and the pain of being a programmer — at the same time!

Spent

A short questionaire game that demonstrates the difficulties of poverty.

PhobosLabs

This site has a few high quality browser games. The one I come back to is X Type, a bullet hell shoot-em up that has ever expanding enemy ship sizes, and never ends. It gets hard fast.

I also like Xibalba, which is a Doom/Wolfenstein style game playable in the browser.

The creator also did a rewrite of quake in 13 kb of javascript

Ember Skull

Fun arcade bullet hell survivors (think vampire survivors) type game. Dodge bullets, and survive as long as you can.

Keep Out!

A webgl/browser based 3d dungeon crawler with proceduraly generated levels.

Master Archer

Addictive arcade game about archery. Reminds me of flappy bird, not in the raw mechanics, but in the way they are both addicting in the same manner.

Cave Noire

Gameboy roguelike that is simple, but very elegant.

Sadly, since romhacking went down, I don't think it's possible to find the translation patch for it, unless they uploaded it to the internet archive.

Gridland

Also by double speak games, and open source gridland is a variant on the match 3 style. During the day phase, you accrue and store resources, and build stuff. During the night phase, you fight.

Swarm Simulator

Open source idle game, playable in browser. No clicking, just watching numbers go up.

The glitched attraction

A fnaf fangame that is close enough to feel like fnaf, but has a twist: Every single level also involves a puzzle. While trying to survive enemies fnaf style. Although I've never played this game, I LOVE watching it on Twitch. I like to call it "Human's can't multitask: The Game".

Touch Some Grass

A wonderful and life changing experience.

I like to link it without the ending title, like https://store.steampowered.com/app/1944240/ because it's funnier when people can't see the game title in the link.

Mole Mania

Gameboy puzzle game. Very high quality.

Warfork

Fork of the older warsow, open source movement shooter. Think quake.

Sadly, it seems to be dead on steam.

Free Rider HD

Simple bike racing game, although the player is very fragile, which adds some difficulty. Playable in browser.

All the maps are user created content.

A Dark Room

Open source idle game, but not quite. It eventually expands beyond watching numbers go up, into a sort of roguelike, where you can wander the world and collect stuff. And die. Die a lot.

A Dark Room was where I first saw the @ symbol used to represent the player character.

this game is really fun