All Zimlets from Zimbra FOSS source and some example server extensions and documentation.
You could dump Zimlets from Zimlet/src/zimlet/ in /opt/zimbra/zimlets-deployed/_dev
Doing so you can find example code used in Zimlets that do stuff that is not (well) documented.
DO NOT INSTALL THESE ON A PRODUCTION SERVER, also you may wish to: zmprov mcf zimbraHttpDosFilterMaxRequestsPerSec 10000
Extension examples are here: ZimbraServer/examples/server-extensions/README.txt