2021 Update. Totara no longer provides their source code to the public. According to the Moodle repository for Totara on GitHub:
«[The Totara source code i]s not being updated because our access to the original repository was terminated shortly after distributing this clone.»
If you’re interested in the Totara distro of Moodle, which is tailored for businesses and includes several additional features like reporting and learning plans, you can
now no longer download the code base.
Totara’s business model is providing hosting contracts and services to Totara users so that they can concentrate on teaching and learning. However, now if you’re interested in a specific piece of Totara or just want to trial the code to compare it to standard Moodle you can do so (with a little technical expertise required).
Totara’s leadership have been involved with Moodle’s own development for years, one of the to the open source Moodle project is Badges.