List of popular software and their alternatives.
Application Free? OSS? Alternative Free? OSS?
Microsoft Windows Linux Mint
Ubuntu
Microsoft Office Libre Office
Adobe Photoshop GIMP
Paint.net
Krita
Adobe Illustrator Inkscape
Adobe Lightroom DarkTable
AutoCAD AutoCAD For Education
FreeCAD (3D)
LibreCAD (2D)
QCAD (2D)
Recommended Software and application.

Operating System

Application Free? OSS? Notes
Microsoft Windows 10 Most user are familiar with Windows ecosystem. It has tons of support and recommened for general purposes.
Linux Mint Linux Mint is a free, easy to use and comfortable GNU/Linux desktop distribution. It is recommended for newcomers of the linux ecosystem.
Ubuntu Ubuntu is the most popular Linux desktop distribution. It is stable and has great software compatibility.

Productivity

Office suite applications.
Application Free? OSS? Notes
Microsoft Office MS Office is the most popular office suite in the world. It is de facto standard among large corporations.
Libre Office LibreOffice is a free and open-source office suite. LibreOffice is compatible with most of the common file formats from Microsoft Office Suite.
PDF viewer and editor.
Application Free? OSS? Notes
Libre Office LibreOffice is a free and open-source office suite. LibreOffice is supports the editing of PDF documents by default and opens them in the LibreOffice Draw.

Creative

Image Manipulation and drawing.
Application Free? OSS? Notes
Adobe Photoshop Photoshop is the industry standard not only in raster graphics editing, but in digital art as a whole.
GIMP GIMP is a free and open-source raster graphics editor used for image retouching and editing, free-form drawing, converting between different image formats, and more specialized tasks.
Krita Krita is a free and open-source raster graphics editor designed primarily for digital painting and 2D animation. .
Design and Vector Graphic Editor.
Application Free? OSS? Notes
Adobe Illustrator Photoshop is the industry standard not only in raster graphics editing, but in digital art as a whole.