The Saint's Tomb is a free 1st level solo adventure for 5e. It's playable in-browser, hosted right here on itch.io. You'll need a character sheet to keep track of your HP, ability modifiers and inventory, but the game will tell the story and roll for enemies.
In this game, you take up a mission to investigate a mysterious figure who has taken an unnatural interest in the funeral of an old priest. You'll fight undead, break into tombs, and (hopefully) save the city!