Taxonomy - Platforms
If your mod comes in two totally separate versions, one for Macs and one for Windows, do not upload them both in one zipped file. Upload them separately, and choose "macOS" for the one and "Windows" for the other. If you have produced a tightly integrated package that can install for macOS or Windows using the same data files (even if there are two installers), then there's no need to artificially split them up for the Mod Depot; use this Platform term in that case.
This refers to the OS that came after the Classic Mac OS -- first known as Mac OS X, later known as OS X, now known as macOS. We do not support Oni for the Classic Mac OS (OS 9 and earlier), so you can assume that all Mac users are in a Unix-based environment which allows mod installation methods such as running .sh (bash) scripts and using Mono to run .NET apps such as OniSplit.exe (though you should keep in mind that Mono is not built-in and needs to be installed by the user).
Sometimes a mod is meant only for Windows systems, perhaps due to the slightly different scripting abilities and engine limits in Oni for Windows. Even if a mod can work on the Mac too, if there's a separate version of the mod produced for Windows, you can upload it under this Platform. You may assume for any Windows-only mod that the user has installed the Daodan DLL and thus has the extensions to Oni which are documented on the wiki.