Back in 2016 when we created this, I was in a quest to find out how TinyPNG did their magic. And this was the result - a PNG image compressor with a custom drag and drop file uploader.
- pngquant - https://pngquant.org/
If you're on macOS, use Homebrew to install like so:brew install pngquant. You should also be able to find compiled binaries on package managers of Linux distros.
Just serve the files with a web server with PHP 5 support ✌️.