Comparison of flashcard software
Comparison of SuperMemo with other flashcard programs requires good knowledge of those programs. SuperMemo World cannot produce such a comparison because it would obviously be heavily biased. Our belief is that no other software comes close to SuperMemo in learning power; however, independent tests (always flawed one way or another) have produced different verdicts. Users of various flashcard programs and users of SuperMemo could best collectively produce such a comparison.
List your contributions below:
Comparison of flashcard applications
A rich source of information can be found here: . Please note that it might be biased as it was done by a co-author of the software they rate as being the best. It's also missing reviews of some of the new flashcard programs. The idea of that website, and the criteria seem very good; however, in this staggering mass of applications, it is often hard to give sufficient attention to individual entries. Consequently, the review of SuperMemo is seriously flawed. Still, you can use this site as a starting point for collaborative contributions of true users of individual applications. Here's another link to a page containing our own review of the above-mentioned SuperMemo review: .
Comparison of spaced repetition software
Here's a link to a wiki page containing some ideas about reviewing SuperMemo and comparing it to other SR programms: 
Here you can find an extensive comparison of various flash card applications for iPhone, iPod Touch & iPad, including SuperMemo UX: 
Below is a list of some better known spaced repetition software:
Menmosyne comes in two different lines: 1.x.x and 2.x.x (the latest line). Line 1.x.x will probably be no longer developed and will soon become obsolete.
Mnemosyne uses a modified version of an older SuperMemo algorithm called SM-2 (which is some 20 years old). Here are some notes on the Mnemosyne algorithm taken from its website :
The Mnemosyne algorithm is very similar to SM2 used in one of the early versions of SuperMemo. There are some modifications that deal with early and late repetitions, and also to add a small, healthy dose of randomness to the intervals. Supermemo now uses SM11. However, we are a bit skeptical that the huge complexity of the newer SM algorithms provides for a statistically relevant benefit. But, that is one of the facts we hope to find out with our data collection. We will only make modifications to our algorithms based on common sense or if the data tells us that there is a statistically relevant reason to do so.
The actual algorithm used in SuperMemo at the moment (May 2012) is called SM-15 and is described here: . The implementation of the SM-2 algorithm in Mnemosyne (both line 1.x.x and 2.x.x) is quite similar to how it worked in older versions of SuperMemo. For example, the user can use 5 grades, and the learning and reviewing modes are not separate. Furthermore, it's worth noting that there is no incremental reading in Mnemosyne, not even a plug-in (add-on) that would offer some kind of simplified version of it. Also, the Mnemosyne community have created a number of free ready-made decks (collections) and plug-ins that users can download.
Mnemosyne is multi-platform. According to its website, there are versions for Windows, Linux, and Mac OS X. For details, see .
This is the program's website: 
Anki also comes in two different lines: 1.x.x and 2.x.x (the latest line). Just like with Mnemosyne, line 1.x.x is likely to become obsolete soon.
Like Mnemosyne, Anki uses a modified version of the SM-2 algorithm  (as we mentioned above, Supermemo 15 uses the SM-15 algorithm). However, unlike in Mnemosyne, in Anki, the SM-2 algorithm has been modified quite considerably. For instance, unlike SuperMemo and Mnemosyne, both Anki 1.x.x and 2.x.x offer only 3 or 4 grades. Also, unlike Supermemo and Mnemosyne, Anki 2.x.x has separate learning and reviewing modes with 3 grades in the learning mode and 4 grades in the reviewing mode.
Anki does have a limited incremental reading plug-in. Moreover, just like Mnemosyne, it offers a number of free ready-made decks and plug-ins that users can download. In particular, Anki offers some plug-ins which considerably facilitate the studying of Japanese and Chinese.
If you want to try and import an Anki deck (collection) into Supermemo, here are some suggestions how to do it: .
Anki is multi-platform. There are versions for Windows, Mac OS X, Linux, FreeBSD, iPhone, Maemo, Android, and an on-line version. For details, see .
This is the program's website: 
Its repetition algorithm is based on an artificial neural network (see also: ). Just like in Supermemo, in FullRecall users can use 5 grades. Also, there are no separate learning and reviewing modes. FullRecall is multi-platform. According to the program's website, there are versions for "Windows, Linux, FreeBSD, Mac OS X (x86), Maemo (beta), and less powerful non-PC versions: Pocket-PC, online on the web, [and] Android (beta)." For details, see .
The latest version of the program can always be found here: