Sites referring to open problems in mathematical research. Those referring to a specific area should be submitted to that category: there is also a recreational category.
In various subjects, compiled by Torsten Sillke.
Elementary unsolved problems in mathematics, listed at the MathPages archive.
A collection of unsolved math problems anyone can contribute to.
A list of unsolved problems published by MathPro Press during 1995.
A list compiled by Eric Weisstein in MathWorld.
Thanks to DMOZ, which built a great web directory for nearly two decades and freely shared it with the web. About us