thanks for your list. appreciated. my question should have been more precise. last time I checked all the Datalog projects I found where either old, unmaintained or have only a single contributor. and that is also true for your examples. I really like Prolog and would love to use Datalog for (RDF) knowledge graph inference.

Then use them! Then those projects will cease having a single contributor or being unmaintained. This doesn't need to be a binary decision (either there is no risk or I won't use it), just choose the project / scope with knowledge that there is some risk in a small community; so internal use rather than client facing, specialized uses, etc.

not sure how using a project adds a contributor. but for the latter - I'm not sufficiently competent at Prolog and friends to meaningfully contribute. I do donate money, though, to projects I regularly use - like for example FreeTube or Linux Mint.