Our research in cooperative systems is directed towards the realization of generic and fully decentralized systems. Our focus is on designing and analyzing Internet-deployed reputation and trust systems, and on cybercurrencies. This research is an outgrowth of our research on Peer-to-Peer systems, which focused on content delivery systems, from file downloading towards real-time video streaming. An important focus of this research was exploiting social groups in P2P systems for use in content discovery, content recommendation, and downloading. Much of these research activities in P2P and cooperative systems are centered around the Tribler P2P file sharing system we have designed and released, that builds on BitTorrent.