Cross-Platform Software

File Managers

Total Commander File manager

Double Commander Open source file manager

7-Zip file archiver

Password Manager

KeePassXC Password manager

Web Browsers

Firefox

Chromium

E-Mail Clients

Thunderbird

Sylpheed Lightweight email client

Network Tools

FileZilla Client FTP, FTPS and SFTP client

Wireshark Network protocol analyzer

Education

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

Anki Anki is a program which makes remembering things easy

Office

LibreOffice Open Source office suite

JabRef A citation and reference management tool

Organizers

Taskwarrior Command line Task Management

Rainlendar Calendar application

Text Editors

Geany Text editor with basic IDE features

Vim Highly configurable text editor

TeX

MiKTeXTeX distribution

TeXstudio An integrated writing environment for creating LaTeX documents

Graphics

GIMP GNU Image Manipulation Program

Inkscape Vector graphics editor

Multimedia

VLC Multimedia player

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

Development

Meld diff and merge tool

Microsoft Visual Studio

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

ROOT C++ data analysis framework

python programming language

Git version control system

SQLiteStudio SQLite database manager

v.Nu HTML Checker helps to catch problems in HTML/CSS