I tried plan9port's mk for a moment out of curiosity. I quickly ran into an annoying usability problem: it compares file mtimes with second accuracy.

https://github.com/9fans/plan9port/blob/cc4571fec67407652b03...

With sub-second build times for individual targets, this causes mk to needlessly recompile files because the target may have the same mtime as the prerequisites.

That looks like it would be relatively straightforward to fix. Attempted nerd snipe?