[gottoupvote]

There's also https://alternativeto.net/, tagged with licencing model

[blooalien]

Great site! That one's been my "go-to" site for this need for many years now. Was especially helpful back when I was new to Linux.

[npteljes]

This was my jam when I switched to Linux, many years ago.

I love it that they updated with pro-contra comments. As software are usually not drop-in replacements to one another, you can learn a lot about the differences before switching. I like it that they also include descriptions, general comments, license and screenshots.

[KomoD]

Personally don't like this one. I don't like the design of the site.

If I'm at a page listing the alternatives, such as https://alternativeto.net/software/mtr

It doesn't have direct links to the alternatives, if you hover over an alternative it shows a "copy link" icon, but that just goes to the same page you are already on, instead you have to press into the alternative's page and scroll until you see a "official links" section