Today, both CentreSIS and FocusSIS have a Moodle integration you just can't get. Oops. I couldn't find the current FocusSIS codebase. CentreSIS asked for my email, and sent a series of emails, one per day, for a couple of weeks; the second or third in the series had the link to the actual download.
I finally found RosarioSIS, yet another fork, which seems to be reasonably well maintained, and published on github. It does have a Moodle integration. It's not perfect, but it's a great start; and it uses Moodle's web services.
So, kudos to the RosarioSIS dev team, and some visibility here.