ImageKit.io - Instant multi-platform image optimization
Promo.com - Every promotion starts with Promo.com.
Resizing.app - Image resizing has never been so simple with free online resizing.app. Convert, optimize, resize images with ease and for absolutely free.
Pixelhunter.io - Free AI image resizing tool for social media
Piio - Generates responsive images so you don't have to optimize
Optimage - Advanced image optimization tool