There is also SuperMemo 18 (https://super-memo.com/supermemo18.html) which is from the same people as supermemo.com except it's a desktop app with way more features but also a much higher learning curve.

If you use SM and you use anki both for a significant amount of time it's not hard to see that SM leaves you with way less reps. Anki is based on the very first version of the SuperMemo algorithm (from ~1990 or so which was the first SRS algorithm ever) known as SM2. Current version of SM uses SM18.