Nine Lives Valley

You play in Terraria, and three other games move in with their own real content, read from your own installed copies while you play.

A wagon of newcomers pulls up by your spawn point. Right-click each one:

• Pierre (Stardew Valley) sells the season's seeds and buys your harvest at Stardew's prices. Plant on Terraria soil and your crops grow day by day with Stardew's own growth times and sprites. Seasons last 7 days, and crops out of season wither.
• Promotheus (Legends of Idleon) promotes you from Beginner to Warrior, Archer or Mage. Idleon's monsters (Green Mushroom, Frog, Bored Bean, Carrotman, Baby Boa, Glublin and more) roam by day, by night and underground. Mining, Choppin, Fishing, Farming and Breeding level up as you do them, and Idleon's AFK Gains window pays you for the time you were away.
• Tabby (Mewgenics) looks after your cats. Adopt strays, take up to three along to fight beside you, and breed pairs at home. Kittens inherit parts, stats and mutations from both parents. Cats age every dawn, and once a cat dies it is gone for good.

Controls: right-click newcomers, crops and cats. V picks a seed, C opens your cats, K shows help, F9 saves a screenshot.

You need: Terraria 1.4.5 or newer, Stardew Valley, Legends of Idleon MMO and Mewgenics, all installed through Steam on Windows. If one is missing the game tells you and that game's part is switched off. Single player. Your Terraria characters and worlds work as they are; nothing in any game's files is changed.

Credits: built with Claude. Uses Harmony (MIT, Andreas Pardeike) and Mono.Cecil (MIT, Jb Evain). Terraria by Re-Logic, Stardew Valley by ConcernedApe, Legends of Idleon by Lavaflame2, Mewgenics by Edmund McMillen and Tyler Glaiel. Unofficial fan project; no game files are included.