I participated in a game jam last weekend about making SHARECART1000 compatible games and decided to share the framework I built for interacting with the system. If you're not familiar with SHARECART1000, I'd recommend reading this page, but the basic idea is that a bunch of games read and write to a single save file with a handful of variables.
I'm not an expert in SHARECART/Construct/anything, so it's probably not the most perfect or full-featured or efficient thing, but I'd love to hear feedback from anyone who thinks they could improve upon it. The one thing that the game jam curators mentioned was a potential issue with my implementation is that it writes the file with LF (Unix) line breaks instead of CRLF (Windows) line breaks, but I'm not sure if there even is a way to specify that in Construct.
You can download my framework on itch.io and check out my entry to the game jam here (though be warned: it's not super impressive because I spent so much more time on the SHARECART framework than the game itself).
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Interesting concept, one filetype to rule them all.