Behind my house flows the Little Creek, which drains rainwater a large portion of Chapel Hill by way of the now-infamous Bolin Creek and Booker Creek. These upstream tributaries of Little Creek regularly flood and frequently damage the Eastgate shopping center and camelot village apartments.
Analyze image data from a nearby web camera, and estimate the water level, both in daylight and at night. From that start, the software could add various other features: Generate web pages that contain the image, the numerical estimate of water level, and some kind of confidence metric in the estimated level. Log the estimated level over time. Send email when the level exceeds a certain threshold. Integrate camera, video capture, analysis software, and web server into a standalone turnkey internet-connected appliance.
In order to be useful to me, the software developed would have to run on Linux and be entirely Open Source. Beyond that, implementation language and libraries/toolkits are relatively unimportant.