Resizing.app - Image resizing has never been so simple with free online resizing.app. Convert, optimize, resize images with ease and for absolutely free.
Aerate for macOS - Ridiculously good lossless image compression
Image Resizer for Windows - Lets you resize images by right-clicking.
Polarr 2.0a - An online photo editor (big data meets Lightroom)
Icecream Image Resizer - Image resizer by Icecream Apps is a program to resize images fast and free. Windows version. Free Download.
Acorn - Acorn is a photo editor built for the rest of us.