Mockuuups Studio - Fast and easy way to create product mockups on macOS, Windows and Linux.
Gyroscope - Gyroscope is a personalized dashboard for tracking your life.
Smartmockups - Create stunning product mockups, easily and online.
CareKit by Apple - Open source software framework for creating health apps
Placeit - Generate realistic product shots in seconds
DNScapy - DNScapy is a DNS tunneling tool. The code is very light and written in Python.