Looks great! I’ve popped the list into ChatGPT to produce a differentiation categorisation for easier 3D soul searching for those unfamiliar with some of the sites 
Would be good to double check just in case the below is wrong!
General and Popular Free Model Sites
- Thingiverse
- Known for its large, free library of 3D printable models. A go-to for hobbyists and beginners seeking community-created designs across many categories.
- Cults3D
- Offers both free and paid models, with a focus on high-quality, curated designs, and a wide range of models from artistic pieces to practical tools.
- Yeggi
- A 3D model search engine that aggregates models from multiple sites, useful for finding specific STL files from across the web.
- Pinshape
- Hosts free and paid models, with community-driven designs and a focus on usability for makers at all skill levels.
- MyMiniFactory
- Community-curated collection with models tested for printability, ideal for finding reliable STL files, especially for miniatures and detailed items.
Premium and Professional 3D Model Marketplaces
- CGTrader
- A vast marketplace for professional-grade 3D models, including both printable STL files and models for CGI, game development, and more.
- TurboSquid
- Known for high-quality 3D models used in animation, architecture, and film; some models can be adapted for 3D printing, though it’s not specifically focused on printable files.
- 3DExport
- Offers a variety of free and paid 3D models for download, often used by professionals needing detailed, high-quality assets.
Specialty and Niche Model Libraries
- NASA 3D Resources
- Provides free, authentic models from NASA, including models of spacecraft and scientific equipment, ideal for educational and scientific projects.
- NIH 3D Print Exchange
- Features models focused on medical and scientific use, often used by educators, researchers, and health professionals.
- Fab365
- Offers a range of unique foldable and articulated designs specifically optimized for 3D printing, excellent for advanced hobbyists looking for functional designs.
Model Libraries with Free & Creative Commons Content
- Sketchfab
- Primarily for 3D artists and animators, it also offers STL files for download. Its 3D viewer is useful for exploring models in detail before downloading.
- YouMagine
- Maintained by Ultimaker, this site features a collection of free STL files with a focus on reliable, print-ready designs from community members.
- STLFinder
- A search engine for finding STL files across many platforms, useful if you’re looking for specific models and want to see options from various sources.
- Instructables
- Provides projects and tutorials, many of which include STL files, making it ideal for DIY enthusiasts who want step-by-step instructions along with model downloads.
Educational and Tool-Based 3D Model Resources
- Tinkercad
- A browser-based 3D design tool by Autodesk, popular for beginners. It allows users to create their own models and share them within the Tinkercad gallery.
- Blender Swap
- A platform for sharing Blender models, often used for CGI but with some models that can be adapted for 3D printing.
- 3DKitBash
- Focuses on printable kits and toys, with unique modular designs that are easy to print and assemble.
Libraries with Highly Specialized and Free Content
- 3D CAD Browser
- A large selection of 3D CAD models, particularly useful for those looking for technical or engineering models.
- Treatstock
- A platform that combines a model marketplace with 3D printing services, allowing users to either download models or have them printed and shipped.
- XYZprinting Gallery
- Free models optimized for XYZprinting’s 3D printers, though compatible with other printers as well.
Model Sources for Creative and Experimental Projects
- Forge by Zheng3
- A collection of whimsical and creative STL files, perfect for hobbyists looking for unique, artistic models.
- Open3DModel
- A mixed library of free 3D models, with categories ranging from furniture to vehicles; not all are optimized for printing but can be adapted.
- Polar 3D
- This educational platform features classroom-focused models and resources for teachers looking to incorporate 3D printing into their curriculum.
Legacy or Lesser-Known Sources for Free Models
- TF3DM
- Offers a mix of 3D models across genres; a good source for varied content, though model quality can vary.
- Archive3D
- Free 3D models of all kinds, often used for architecture and design; some may need modification for 3D printing.
- 123Dapp Gallery
- Originally created by Autodesk, it now hosts a variety of models, though the platform is no longer updated.
For Historical and Scientific 3D Scans
- Smithsonian 3D (3d.si.edu)
- Offers detailed 3D scans of museum artifacts and cultural items, great for historical and educational projects.
- Threeding
- Contains museum artifacts and archaeological models, with a mix of free and paid options, particularly useful for academic purposes.