This is part of a talk given at SEAPUG on April 4, 2024.
https://github.com/pgextensions
https://www.postgresql.org/docs/current/extend-pgxs.html
https://www.postgresql.org/docs/current/xfunc-c.html
https://www.postgresql.org/docs/current/xoper.html
https://www.postgresql.org/docs/current/xtypes.html
PGXN - https://pgxn.org
PGXMAN - https://pgxman.com