The two are very similar. I wrote the first version of this almost 10 years ago and only became aware of the existence of Sourcetrail while doing the rewrite a few months back.

On the surface - there is a difference in languages. Sourcetrail explicitly supports C/C++/Java/Python while Code2flow supports Python/JS/PHP/Ruby.

I would love to give code2flow the capability of Sourcetrail but would need to feel very good about it making money before I devoted that time to it.