Just a decent list of popular image optimisation tools available.

Remove.bg

https://www.remove.bg/
Remove background from images.

Tinypng

https://tinypng.com
TinyPNG optimizes your PNG images by 50-80% while preserving full transparency!

Imageoptim

https://imageoptim.com
Removes bloated metadata. Saves disk space & bandwidth by compressing images without losing quality. Excellent for web images.

Gulp and Grunt image

Grunt https://www.npmjs.com/package/grunt-image
Gulp https://www.npmjs.com/package/gulp-image
Multi purpose

Pngcrush

https://pngcrush.com/
Pngcrush is a free and open-source command-line utility for optimizing PNG image files. It reduces the size of the file losslessly

Compressor

https://compressor.io/
4 file formats are supported. Optimize and compress your images online. Compressor is a lossy and lossless photo compression tool.

Kraken

https://kraken.io/web-interface
Optimize your images with blazing speed using powerful API and online web interface. Limited to 1mb file size for a free account. Go pro for everything.

Squoosh

https://squoosh.app
Any images format. Compress and compare images with different codecs, right in your browser. Extremely efficient.

Photopea

https://www.photopea.com/
The online photoshop.
Read more about that solo developer who did it all by himself.
https://medium.com/@ivan.kuckir/hi-i-am-author-of-photopea-photopea-exists-since-september-2013-but-sketch-support-was-added-7942223b47b9

Uploadcare

uploadcare.com
File uploads, media processing, and adaptive delivery for web and mobile

Imgix

imgix.com
Powerful image processing, simple API

Edit:

Ipiccy

http://ipiccy.com
Suggested by: Serkan Bektas

Comment below the tools you use.

Let's grow this list.