Miiverse, Nintendo's social network, is now accessible on PC and mobile devices by going to the Miiverse website through an internet browser. The beta version includes access to your Activity Feed, where you can view updates from friends and give them Yeahs. You'll also be able to browse communities and check your notifications. However, the current version of Miiverse for PC and mobile is read-only. You won't be able to post updates, nor will you be able to register for the service. These features are exclusive to Wii U only, for now.
Going forward, Miiverse access will expand to 3DS. "We are also planning to make available a system update for Nintendo 3DS to allow its users to view and post content on Miiverse on the system within this year," Nintendo announced in an investors note. "This will facilitate user communication about Nintendo 3DS games and help users enjoy them more deeply. At the same time, the more people take advantage of Miiverse, the more deeply and correctly they will understand the charm of the other platform, Wii U."