I briefly toyed around with Kcgi when I was setting up a neat little Libravatar[0] implementation[1] I found.

[0]: https://www.libravatar.org/

[1]: https://github.com/tleguern/libravatar.cgi

I eventually dropped that implementation in favor of a pure static implementation in pure Nginx, but it was less unpleasant to work with than other (Fast)CGI libraries I've tried.

It goes well with the rest of the BCHS stack[2] of OpenBSD, C, OpenBSD httpd, and Sqlite. Some say that BCHS is impractical due to an aversion of writing C for server-side applications, but I find it perfectly adequate for tiny CGI programs that don't need a big framework.

[2]: https://learnbchs.org/