Cross-Platform Software

Internet Browsers

Firefox Windows Linux Android

Pale Moon Windows Linux

Chromium Windows Linux

E-Mail Clients

Sylpheed Lightweight email client Linux Windows

Security/Privacy

KeePassXC Password manager Linux Windows

Wireshark Network protocol analyzer Linux Windows

File Managers

Total Commander File manager Windows Android

Double Commander Open source file manager Linux Windows

Text Editors

Geany Text editor with basic IDE features Linux Windows

Vim Highly configurable text editor Linux Windows

Office

LibreOffice Open Source office suite Linux Windows

MuPDF Viewer of pdf and xps files Linux Windows Android

Graphics

GIMP GNU Image Manipulation Program Linux Windows

Inkscape Vector graphics editor Linux Windows

Audio and Video

VLC Multimedia player Linux Windows Android

Audacity Easy-to-use, multi-track audio editor and recorder Linux Windows

Learning

GoldenDict dictionary supporting multiple formats (StarDict/Babylon/Lingvo/Dictd) and online dictionaries Linux Windows

Anki Anki is a program which makes remembering things easy Linux Windows Android

Software
Development

NetBeans IDE Open-source IDE supports Java, C/C++, php, JavaScript, HTML5 Linux Windows

ROOT C++ data analysis framework Linux Windows

python programming language Linux Windows

Git version control system Linux Windows

Meld diff and merge tool Linux Windows

SQLiteStudio SQLite database manager Linux Windows