- Browsers are XSLT (1.0) processors.

- Xee: https://github.com/Paligo/xee

- xrust: https://docs.rs/xrust/latest/xrust/xslt/

- XJSLT (compiles XSLT to JS): https://github.com/egh/xjslt

Xee is WIP AFAIK and I don't know the maturity of xrust and XJSLT.

Yeah... I posted too quickly: I want XSLT 3. The 1 & 2 specs are good first attempts, but are very difficult to use, effectively. As another poster also commented: it'd be nice if the implementation wasn't tied to XML, as well!

Also, I want a cookie & a pony.

I guess Xee is the most promising option then :-) But indeed not ready yet.

I only know libxslt, but it's XSLT 1.0 and some of EXSLT. I don't recommend.

libxslt, despites being available widely, must not be recommended. https://lwn.net/SubscriberLink/1025971/73f269ad3695186d/