I am surveying small, locally streaming cameras for applications in art installations such as capturing video to process, present, or to use for tracking, analysis, or interaction.
Recently I tested the Nextech mini wifi camera
This is a good example of a Raspberry pi approach that focusses on low latency. This would be particularly helpful when using for tracking. The Nextech camera
The system above uses UV4L which looks like an excellent tool kit. It has a feature that allows you to capture an HDMI output and stream that. So you could for example make an openframeworks application using processing a video camera feed and then forward out the fullscreen output of that application as a low latency MJPG stream.
Another approach would be to send video via NDI with Dicaffeinate. This approach would be my preference due to the ease of integrating NDI in other frameworks and video tools - TouchDesigner, OpenFrameworks etc.