See "Little Snitch for Linux" https://news.ycombinator.com/item?id=47697870

Also:

Little Snitch is not there to replace OpenSnitch. It's just an additional option you can choose from. Some people might prefer it, others not.

https://news.ycombinator.com/item?id=47701918

But I currently can't make the entire project Open Source. My other option would be to keep it completely private (wrote it mostly for myself in the first place).

I think it's still better to make it public and only partially Open Source so that some people can benefit from it. If you don't trust us, that's completely reasonable, just don't install it.

https://news.ycombinator.com/item?id=47701740