A project I wish existed is an open source competitor to Google Earth's automatic generation of 3D models from satellite images. Their generator is pretty smart and even generates pretty good approximations of trees, bushes, streetlights, and so on. This is very useful when you need to figure out 360° line-of-sight from a point in space (i.e. a viewshed) for things like planning where to put RF antennas as topographic maps don't take vegetation or other obstructions into account.

Google Earth even has built-in viewshed generation which uses their 3D model data (works great), but unfortunately the 3D model layer only seems to exist for fairly populated areas (probably because it's computationally expensive) - so doing RF planning in rural areas requires more traditional legwork.

So it would be cool for a project to provide similar functionality for OpenStreetMap using this public satellite data. OpenStreetMap does have 3D modeling support but last time I looked it seemed pretty focused on buildings and people hand-editing the data.