Use the list-box to select a new section. This link does not work. I will update it if I discover where it has moved to. A good variety of problems, in an interactive format. You can have the solution with the solution shown in several formats.
People can add new problems to the site.
Hitachi Two new problems each week. 60 problems in total. The site uses both Japanese and English languages. Jan van der Steen 60 problems. Koutek tsume-go 2 problems, with ample discussion in Czech.