Kroki provides a unified API with support for BlockDiag (BlockDiag, SeqDiag, ActDiag, NwDiag), C4 (with PlantUML), Ditaa, Erd, GraphViz, Mermaid, Nomnoml, PlantUML, SvgBob and UMLet... and more to come!

pngquant is a command-line utility and a library for lossy compression of PNG images.

The conversion reduces file sizes significantly (often as much as 70%) and preserves full alpha transparency. Generated images are compatible with all web browsers and operating systems.

Pngquant is a free, open source and cross-platform command-line lossy PNG compressor. It is based on a portable libimagequant library and is written in C99. It reduces the file size significantly by converting the PNG image to more efficient 8-bit PNG format and preserves full alpha transparency. As you may already know, 8-bit PNG files are often 60-80% smaller than 24/32-bit PNG files. The images compressed using Pngquant are fully-compatible with all web browsers and operating systems. Pngquant can compress one or multiple images at once.

"X11 image viewer aimed mostly at console users" (cit.); with no fancy GUI, it is controlled via commandline arguments and configurable key/mouse actions.

A library and a program to display JPG, PNG, GIF or BMP images in the terminal using ASCII characters.

Software suite to create, edit, compose, or convert bitmap images; it handles many file formats (including PDF and SVG) and provides processing tools to "resize, flip, mirror, rotate, distort, shear and transform images, adjust image colors, apply various special effects, or draw text, lines, polygons, ellipses and Bézier curves".

A vegetable-picking robot that uses machine learning to identify and harvest a commonplace, but challenging, agricultural crop has been developed by engineers.

Lazygal is another static Web gallery generator. It is command line based, uses a reusable engine and is lazy, meaning that it regenerates only parts that have to be regenerated. There is support for many interesting features like subgalleries, EXIF information, theming, and custom folder meta data. Included themes are pure XHTML and CSS.

Flameshot is an easy to use, open source, Qt-based screenshot utility which is adept at capturing custom areas of a desktop.