Blender is the free and open source 3D creation suite.

Synfig Studio is an open-source 2D Animation Software for Windows, Linux and MacOS.

Ardour is an open source software for recording, editing, and mixing audio on Linux, macOS and Windows.

Audacity is an easy-to-use, multi-track audio editor and recorder for Windows, macOS, GNU/Linux and other operating systems.

QucsStudio is a free and powerful circuit simulator

FreeCAD is your own 3D parametric modeler.

LibreCAD is a free Open Source CAD application for Windows, Apple and Linux.

QCAD is a free, open source application for computer aided drafting (CAD) in two dimensions (2D).

KoboToolbox is a data collection, management, and visualization platform used globally for research and social good.

Orange Data Mining - Fruitful and Fun is an open source software for machine learning and data visualization.

Weka is a collection of machine learning algorithms for data mining tasks.

GRASS GIS offers powerful raster, vector, and geospatial processing engines in a single integrated software suite.

QGIS is a free and open source Geographic Information System.

GNU Image Manipulation Program (GIMP) is a cross-platform image editor available for GNU/Linux, macOS, Windows and more operating systems.

LyX is a document processor that encourages an approach to writing based on the structure of your documents (WYSIWYM) and not simply their appearance (WYSIWYG).

TeXstudio is an integrated writing environment for creating LaTeX documents.

SIMBRAIN is a free tool for building, running, and analyzing neural-networks (computer simulations of brain circuitry).

Beaver Notes is the privacy-focused, open-source note-taking app for all your needs.

GNU Octave is a high-level language, primarily intended for numerical computations and provides a convenient command line interface for solving linear and nonlinear problems numerically, and for performing other numerical experiments using a language that is mostly compatible with Matlab.

Maxima is a system for the manipulation of symbolic and numerical expressions, including differentiation, integration, Taylor series, Laplace transforms, ordinary differential equations, systems of linear equations, polynomials, sets, lists, vectors, matrices and tensors.

Scilab is an open source option for numerical computing that runs across all the major platforms: Windows, Mac, and Linux included.

Apache OpenOffice is the leading open-source office software suite for word processing, spreadsheets, presentations, graphics, databases and more.

LibreOffice is a powerful and free office suite, a successor to OpenOffice(.org), used by millions of people around the world.

GNU PSPP is a program for statistical analysis of sampled data. It is a free as in freedom replacement for the proprietary program SPSS, and appears very similar to it with a few exceptions.

Jamovi is another open-source alternative for search SPSS but with a fancy easy-to-use interface and smooth learning curve for students and beginners.

JASP is considered one of the strongest competitors for SPSS.

OpenBoard is an open source cross-platform teaching software for interactive whiteboard designed primarily for use in schools and universities. 

Inkscape is professional quality vector graphics software which runs on Linux, Mac OS X and Windows desktop computers.

Natron is an open source compositing software for VFX and motion graphics.

HandBrake is a open-source tool, built by volunteers, for converting video from nearly any format to a selection of modern, widely supported codecs.