BNC inputs: 2 sets of 5 BNC connectors each, which can be used for analog computer inputs, or for additional Component video sources. Add all of that up, and you have a whopping 8 high resolution (computer, component and digital - HDMI) inputs, plus the four lower resolution ones (the composite and S-video).
Other input/outputs: There are two RS-232 connectors - One is mandatory, and connects to the projector (Optoma provides a short cable, and an extension, but in most mounting situations, you will need longer cables). The second one can be connected to external control devices, such as a room controller (ie. Crestron, AMX...), computer, etc, for remotely controlling the projector functions.