YalerTunnel is a simple relay infrastructure based on Linden Lab’s Reverse HTTP. All it takes is a few lines of code to make your embedded system accessible behind a firewall, a NAT or a mobile network gateway. Yaler just reverses the connection and forwards the request to you via the REST API. It has been engineered for high performance, maintainability, robustness and is implemented with Java’s non-blocking sockets, hierarchical state machines, and Design by Contract. All of this in a nifty little open source application!
Source: https://thehackernews.com/2010/11/remotely-access-devices-behind.html