“mixi” is the most popular Japanese social networking service (SNS) with 16.3+ million registered users. It lets users create profiles, make friends with other users, post diaries, discuss in several communities, share pictures and music with friends, etc. In addition to those basic features, “mixi apps” lets social application providers develop applications that use social graphs formed in mixi, and provide these applications to mixi users. The team has released an open beta of “mixi apps, ” which is based on OpenSocial.
More info: mixi Platform