I have been working on a general purpose site for cognitive tests, for informational purposes and out of interest. It's also the first thing I thought of doing after learning some Flash.
One of the tests I decided to include initially is an n-back task variant; as per http://news.ycombinator.com/item?id=176264 , NewScientist wrote about a recent publication using an n-back task, so I thought I should demo while it's still fresh in memory. Forgive its simplicity (and again, it is a variant), but as always, I'd love to hear your feedback.
http://cognitivefun.net
A simple variant of the n-back task (adjustable between 2 to 5-back) is here: http://cognitivefun.net/test/4 Test 1 is a classical reaction time test.
I haven't had time to think of how to track and display progress, so it just loads the stats. Suggestions are welcome. If Test 4 is stable I'll be working on other tests, like interference tests and counting and such.