Most classic roguelikes are free and many even open source. It is a great genre and if you take time to learn one of them you’ll be at home in any. They are all played in micro-turns so time only advances when you make inputs. That means you can get up at any time without having to pause the game. They have many other features mostly unique to them, too. For instance, in basically all of them everything stays the way you leave it. Items on the ground don’t despawn after a while. Monsters can also pick up and use your items, though.

Cataclysm: Dark Days Ahead is one of my favorite games of all time. You can explore realistic towns and forests after the apocalypse. For instance, you can find most of the items that would be in a real kitchen in an in-game kitchen and use them to craft a staggering amount of stuff. While you’ll mostly see zombie variants, there are enough different horrifying things to encounter that every run is different.

The controls of C:DDA are numerous, though. It may not be a friendly starting point if you have no experience with anything like it. I’m not sure what to recommend for that. Brogue is easy to get into but pretty shallow. Dungeon Crawl: Stone Soup might be a decent introduction to the genre.