I haven't played A Town Uncovered and there aren't really a whole lot of games that match the sheer amount of content, exploration, or detail that Summertime Saga has, but I'd recommend a few. These three were the first to come to mind and should run on Mac without any issues.
Princess Trainer:
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Complete game with a TON of content. Many places to explore, good 2D art, and side quests. This is my top recommendation in terms of something that is comparable with Summertime Saga - it is actually a good video game. Arguably one of the best in general that you'll be able to find on f95.
Lab Rats:
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Complete game with solid amount of content. The 3D art isn't my favorite, but I'd consider it passable. This is one of the few mind control games that doesn't make the MC seem like a rapist. You can play with a day limit or set it to end whenever you choose, so in many ways it plays out like a sandbox VN.
Mythic Manor:
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Still in development but actually has a lot of content. The 3D models are pretty good and if you don't mind "mythical girls" then its definitely worth trying out.
In general, Ren'Py games have Mac versions or can easily be converted. Here's the tutorial for converting a game if you're having issues:
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You'll need to download additional software in order for other types of games to be able to run on Mac and unfortunately there's no getting around it. There's a bit of a learning curve here no matter what. I won't go into that since it seems like you just wanted some recommendations, but if you have any questions I might be able to help.
