The list of the top Desktop Applications with an Open Source license.

Office suite

Libre Office Platforms: Linux/Mac/Windows onboarding Non-programming tasks: Documentation,

Web browser

Firefox

Chromium

Media Player

VLC of Videolan

Popcorntime

Image editing

Gimp

Blender

Digikam

Image Magick

Inkscape

Communication

Jitsi

Audio recording and editing

Audacity audio software.

Ardour

Traverso DAW

Notepad++ Windows only text editor. Written in C++.

Partially taken from this list where there are a few more.