This page lists various games that can be played via the web brower – many of which I have admittedly yet to play.
Simple
Wordle – every day guess a 5-letter word whilst avoid being one of hundreds of millions spamming social media with their results (nobody cares about your wordle guesswork)
Conway’s Game of Life
This isn’t a game in the traditional manner. It’s a simulation of swarm behaviour, automatons and patterns (It’s actually Turing complete). Once you mess about it with it from randomizing starting sequences through to patterns created, it’s pretty cool. One of my favourite youtube channels, Numberphile, interviews John Conway (a few times) on the subject; shown below. Here’s the game: https://copy.sh/life