There already was MiNTNet support for cheap USB2LAN adapters based on the Asix AX88772 chip. However, these weren't usable under plain TOS because there is no driver (e.g. for STinG) for them. This is why I ported uip-tool to work with these USB2LAN adapters. You probably already know that uip-tool allows you to upload and download files to/from your Atari via a web interface or an API.
A suitable USB addon card supported by the USB stack for TOS is required. Of course, I recommend the Lightning VME for MegaSTEs and TTs.
You can find my port of uip-tool here: https://bitbucket.org/czietz/uip-tools/downloads/. Source code is also available on Bitbucket. I tested it with the Lightning VME on an Atari TT, achieving ca. 130 kB/s download rate. Please read the thread about uip-tool to learn how to use it: viewtopic.php?f=14&t=27365. Also questions not related to the USB support (but e.g. to the web interface) are probably best posted there.
While this ran stable during my tests, I still consider it "proof of concept" or beta. If you want to develop it further, I'm happy to accept any patches.
PS: Only the USB.PRG driver (USB stack) and the driver for your USB card (BLITZ*.PRG in case of the Lightning VME) are required in the AUTO folder. My port of uip-tool brings loads its own internal Ethernet driver; so please don't use ETH.PRG from the USB4TOS distribution.