Marble
Marble – free and open source, cross platform software that represents a virtual globe and an atlas of the world
Google Earth
Google Earth – free and crossplatform a virtual globe that provides geographical and cartographic information
KStars
KStars – free and open source, cross-platform virtual planetarium that shows the night sky from anywhere on our planet
Stellarium
Stellarium is a free and open source, multi-platform desktop planetarium, renders 3D photo-realistic skies in real time with OpenGL
Playary
Playary is a free multi-platform program for watching free movies and listening to free music and podcasts
Scorched3D
Scorched3D is a free and open source, multi-platform simple turn-based artillery strategy game in real time
Duplicati
Duplicati is a free and open source, multi-platform client-server program for creating encrypted backups for storage in the cloud/remote servers
Manga Reader
Manga Reader is a free and open source program for reading manga/comics from a local library
Redshift Control Plasma
Redshift Control Plasma – free and open source applet for automatically adjusting color temperature of screen depending on time of day in KDE Plasma
Curtail
Curtail is a free and open source, simple and useful software for compressing images in Linux