I have been working on Android platform for three years. I have several apps on Google Play Store. I work for a company which use many technology in our products. I have worked with these one: live video streaming, p2p protocol, upnp, udp punch hole, mqtt, websockets, nodejs, mysql, mongodb, system admin, ffmpeg, android video player (encrypted audio & video), android ndk, amazon web service, google app engine. I could do backend api server as well (node.js & mongdb or mysql, ...)