Stars/commit info is fed directly from github. If a project doesn't use github it will need to demonstrate it has an an active user base somehow.
CertSage probably doesn't qualify for this list based on popularity just yet (?) but you should add it to ACME Client Implementations - Let's Encrypt in order to build up your user base.
There are obviously hundreds of ACME clients, but not this is not an exhaustive list, it's just the popular ones. I'd consider having a tab for less popular projects (it would need a flag in the data set to indicate popular/not popular) but I'm probably not motivated to populate the data myself so would expect each project to add themselves.
Certify (the command line and service, and the new Web UI) does indeed run on Linux and Mac OS but that's actually a mistake including that just now, thanks for raising it.