The GAM Cheat Sheet gives a summary of commands for the GAM tool that allows management of Google Apps domains.
The current version is v1.52 (21 March 2018) for GAM version 4.40.
Ross Scroggs has an advanced/extended version of GAM with additional functionality not available in GAM. This cheat sheet lists this additional functionality.
Unfortunately this version is way out of date - the latest is v0.1 (11 January 2017) for GAMADV-X 4.39.14 versus GAM 4.03.