Antichamber - "A game with half of the attention to detail and imagination Antichamber has would be a smash hit - this bare-bones first-person puzzler is one of the most thought-provoking, engaging, and challenging video games ever developed.
KiCad - A Cross Platform and Open Source Electronics Design Automation Suite
The Stanley Parable - The Stanley Parable is an Action, First-person Perspective, Puzzle-Platform, Exploration and Single-player video game created and published by Galactic Cafe.
Proteus PCB design - Proteus PCB design combines the schematic capture and ARES PCB layout programs to provide a...
The Talos Principle - Philosophical first-person puzzle game.
QUCS - Qucs, briefly for Quite Universal Circuit Simulator, is an integrated circuit simulator which means you are able to setup a circuit with a graphical user interface (GUI) and simulate the large-signal, small-signal and noise behaviour of the circuit.