I am and all my life have been a Linux user, I have nothing against Windows or MacOS, I just like Linux, and lately I have been experimenting with Windows in a virtual machine and I don't really know much open source software there apart from the one that is cross-platform like Firefox or Joplin.
At the moment I know:
Flow Launcher: It's a typical rofi style launcher, although I'm not a TWM user I like to just press super and type the first letters of the program I'm looking for to open it.
Lively Wallpaper: A program to have animated wallpapers, in the style of Wallpaper Engine.
Edit: I want to clarify that I read all the comments, I only respond to some because many times I have nothing to contribute to many of them because I don't know what to comment. Thanks to all of you for providing your lists of programs, I will be sure to try as many as I can because they are great, at least I know what to install if I use Windows one day!
Scoop looks cute, but if I'm reading it right the manifest (where the pre-install and hash is) isn't itself signed. It presents some neat-o attack space in addition to the supply-chain attack (always, always cringe whenever installers go out and automatically find dependencies for you without you firmly specifying source) make me think this one has some work to do yet. By comparison, prior art for both of those existed in Linux land for about 2 decades, along with simple local repo caching.
I see there's talk of merging or feeding into either choco or winget already, despite the loss of superior layout it has over choco or the superior packaging and management it has over winget .
Scoop is neat, but it could look to its counterparts for improvement potential.