Squoosh is an image compression web app that allows you to dive into the advanced options provided by various image compressors.

Crunch is a tool for lossy PNG image file optimization. It combines selective bit depth, color type, and color palette reduction with zopfli DEFLATE compression algorithm encoding using the pngquant and zopflipng PNG optimization tools.

JavaScript crusher, code minification

RegPack is a packer intended for use on minified Javascript code.
It is mostly suited to small size constraints (1kb, up to 4kb).

Trimage is a cross-platform GUI and command-line interface to optimize image files via optipng, pngcrush, advpng and jpegoptim

PunyPNG is a free website optimization tool that dramatically reduces the file size of your images without any loss of quality.

This is a web interface to compress your JavaScript or CSS.