Anki

Anki is a popular, free, user-friendly, open source, and multi-platform spaced repetition application. It uses a modified version of Algorithm SM-2 originally used in SuperMemo.

Even though SuperMemo has always had freeware versions available, Anki is free in principle. Soon after emerging, it beat SuperMemo in popularity.

Here is a high quality review of both programs: "My Comparison Between Anki and SuperMemo", written by a user of both programs. Objectivity in reference to SuperMemo is hard to find due to program's complexity that goes well beyond the rudimentary needs of a casual users. Superficial understanding of SuperMemo is the main problem in similar comparisons. Even though the author admits a degree of bias, his take on SuperMemo is excellent despite having only 8 months of experience with the program.

This glossary entry is used to explain "History of spaced repetition" by Piotr Wozniak (June 2018)