Information Assets with Identifiers in Public Namespaces. [RFC4452] (section 3) defines an "info" registry of public namespaces, which is maintained by NISO and can be accessed from [http://info-uri.info/].
Access to data available from mail servers
Real-Time Streaming Protocol (RTSP) over TLS
Real-Time Streaming Protocol (RTSP) over unreliable datagram transport
Extensible Messaging and Presence Protocol