I’ve run across a couple sites.

https://www.opensourcealternative.to/

https://github.com/sereneblue/awesome-oss

https://opensourcesoftwaredirectory.com/

https://opensource.com/resources

https://www.techradar.com/best/best-open-source-software

Tangentially related: https://github.com/awesome-selfhosted/awesome-selfhosted

https://noted.lol/

Pretty much the opposite of what you asked for but good to know: https://en.wikipedia.org/wiki/List_of_formerly_open-source_or_free_software

@chirospasm@lemmy.ml beat me to the punch with alternative.to