AlternativeTo is a site I use quite a bit. Personally I use it when I get fed up with an Android app having too many ads / creepy network behavior or want to find a self-hostable version of a freemium service.
It has filters for free, open source, platform type, etc. From my understanding it’s all crowd sourced, so if you disagree with a rating put in a vote! Sharing this in hopes that others find it as useful as I do.
If you know of similar or better resources I would love to hear about them.
Edit: many people are noting that the comments and reviews are out of date. I agree! Despite that I still find it to he useful. It would be great if this little bit of visibility gets more folks engaged over there to improve it.
AlternativeTo is crowdsource, so one individual might find software A as suitable alternative, while others are not.
The same way that some people find GIMP enough to replace Photoshop, while others prefer Affinity Photo, Paint.NET, or Photopea.
I personally find so many cool underrated FOSS software, such as Inochi2D, AB Download Manager, Miria, OpenUTAU, Our Paint, Mihon, and Wick Editor.