The closest library would probably be pngquant. Though I haven't compared results with TinyPng. - Source: Reddit / about 2 months ago
Pngquant - Apply lossy compression on PNG files with or wi. - Source: dev.to / 20 days ago
All images have to have 256 indexed colors, the way I do this is using pngquant. - Source: Reddit / 15 days ago
ImageOptim - Faster web pages and apps.
FastStone Photo Resizer - Convert and Rename images in batch mode Support JPEG, BMP, GIF, PNG, TIFF and JPEG2000
TinyPNG - Make your website faster and save bandwidth. TinyPNG optimizes your PNG images by 50-80% while preserving full transparency!
ImageMagick - ImageMagick is a software suite to create, edit, and compose bitmap images.
PNGGauntlet - -Combines PNGOUT, OptiPNG, and DeflOpt to create the smallest PNGs
JPEGmini - JPEGmini - The Photo Optimization Tool Trusted by Tens of Thousands Image Perfectionists