DN42 – big dynamic VPN, which employs Internet technologies (BGP, whois database, DNS, etc). Participants connect to each other using network tunnels (GRE, OpenVPN, Tinc, IPsec)
Tools
IP Hub – IP lookup website featuring Proxy/VPN detection
RIPEstat – web-based interface that provides everything you ever wanted to know about IP address space, Autonomous System Numbers (ASNs), and related information for hostnames and countries