UDP Bus — Open Source VPN App

android-udp-bus is an application to create UDP forwarders, hubs and other tools. To aid building VPNs, video streaming and other tricky network uses.
Features: * Binding UDP socket on specified port and exchanging traffic between all known peers * Exchanging traffic between multiple UDP sockets * Remembering specified number of peers that have sent us some datagram, with optional expiration policy * Directly specifying peers to send datagrams to. Combined with remembering, it allows using the application as UDP forwarder. * Joining multicast groups, setting TTL, TOS, read and write buffer sizes and other socket options. * Periodical sending of hardcoded datagrams to specified peers (e.g. to keep NAT open) * Displaying of detailed statistics of the traffic * Starting multiple isolated hubs, each with distinct set of ports. Can even act as a simplistic load balancer due to SO_REUSEPORT. The application does not send datagrams back to sender.
Limitations: * UI is not user-friendly. * Not all features are exposed in GUI - you may want to add some undocumented fields to the JSON manually. * Not very optimised for speed or latency. It may be slightly slower than socat udp4-l udp. * Not everything is tested yet * Documentation is lacking