List of Free Open Source Alternatives to Adobe Products

In addition to the solutions mentioned in the linked post, my personal suggestions:

FOSS alternatives to Adobe Lightroom:

darktable - darktable is an open source photography workflow application and raw developer. A virtual lighttable and darkroom for photographers. It manages your digital negatives in a database, lets you view them through a zoomable lighttable and enables you to develop raw images and enhance them.

RawTherapee - RawTherapee is a powerful, cross-platform raw photo processing system, released as Free Software (GPLv3). It is designed for developing raw files from a broad range of digital cameras and targeted at users ranging from enthusiast newcomers who wish to broaden their understanding of how digital imaging works to professional photographers.

Not FOSS but a free image editing application that is easy to use (Windows only):

Paint.NET - Paint.NET is image and photo editing software for PCs that run Windows. It features an intuitive and innovative user interface with support for layers, unlimited undo, special effects, and a wide variety of useful and powerful tools.