PopsiGames
Cataclysm: Dark Days Ahead is a turn-based survival roguelike set after a disaster. You start in a world full of dangers, scavenge for food and gear, craft tools and vehicles, build a shelter, and try to survive threats that range from wild animals to the undead and worse.
It is known for depth. Bodies have injuries, hunger and fatigue, items have weight and volume, and you can craft, mutate, drive and fight in countless ways. You can play with text graphics or with a tile set, and many experimental builds and mods are available. The learning curve is steep, so reading the in-game help first is a good idea.
The game is free and open source, developed by a large community. There are no ads, accounts or purchases.