Google has released a massive dataset of building footprints, extracted from high resolution satellite imagery:

The dataset contains 1.8 billion building detections, across an inference area of 58M km2 within Africa, South Asia, South-East Asia, Latin America and the Caribbean.

1.8 billion features is enormous, and it doesn’t even cover North America, Western Europe, most of China, Japan, or Australia. Incredible stuff, licensed under CC-BY-4 and ODbL.