Computer

are often used to realize the notion of places as well as for proximity-based friend or interest matching. In this work, we extend this by the ability to create and manage groups with location and time restrictions regarding their visibility and ability to be joined. Its main contribution is the design and reference implementation of the reusable MobilisGroups service as part of the Mobilis platform, an XMPP-based service environment for developers of mobile social software. Location-based group formation furthermore links the physical and the virtual world by creating incentives to be at a certain place at a certain time and complements the two approaches mentioned above. Keywords-social networks; group formation; XMPP; social software; mobile computing; Android I