One thing which I appreciate a lot about FreeBSD is that the source code of all CLI tools installed on the system is available under /usr/bin/src, which was a big help for implementing all psutil APIs. OpenBSD source code is also available but it uses CSV and I am not sure it includes the source code for all CLI tools.

I think he means /usr/src/bin on FreeBSD, which is the same for OpenBSD (as well as /usr/src/usr.bin, /usr/src/sbin, etc.). Source code can be downloaded without CVS by extracting the src.tar.gz from any mirror/CD into /usr/src.

This is good news - I have a lot of stuff queued up to port now!