A wearable camera time machine, this Raspberry Pi Zero W extension board (development and wearable versions shown) provides circuitry to power the Pi from a tiny 3.7V LiPo battery and also includes USB charging, battery monitoring, software controlled shutdown, user indicators/buttons and more.
Interesting technical details about the module available in this Mobile Raspberry Pi 3/Zero W: Tips and Lessons Learned post.
A walk-through of the hardware and the embedded system API, along with some actual footage from the device: