Launchpad

Launchpad.net is the open source development forge used by Ubuntu, Canonical, and a number of well known open source projects.  It uses the "Ubuntu SSO", which has experimental 2FA based on OATH HOTP (unlike the more familiar time-based OAUTH TOTP).  Google Authenticator does HOTP just fine.

You enable 2FA on your Canonical SSO account by joining the Launchpad Team "sso-2f-testers" at https://launchpad.net/~sso-2f-testers

Using Canonical SSO 2FA is documented at https://help.ubuntu.com/community/SSO/FAQs/2FA