There's a black box. You can shoot in and watch, where the shot leaves the box. In the box, crystals are reflecting the shots. You have to guess where the crystals are hidden, by watching your shots.

PyBridge lets you play the card game of contract bridge, with human players, over the Internet or a local network. The PyBridge project aims to provide a featureful cross-platform alternative to existing online bridge services.

vnStat is a network traffic monitor for Linux. It keeps a log of daily network traffic for the selected interface(s). vnStat is not a packet sniffer. The traffic information is analyzed from the /proc filesystem, so vnStat can be used without root permissions.

EdenMath is a scientific calculator. It does standard arithmetic, probability, and trigonometric functions.

PulseView is a GUI for sigrok that supports logic analyzers, oscilloscopes, and MSOs.

iotop does for I/O usage what top(1) does for CPU usage. It watches I/O usage information output by the Linux kernel and displays a table of current I/O usage by processes on the system. It is handy for answering the question "Why is the disk churning so much?".