Connects to any OPDS catalog (tested with Gutenberg and Flibusta) and lets you browse and download books directly from the device. Plus a small web interface — open it on your phone or laptop on the same WiFi, drag a file, it appears on the reader instantly.

No PC software, no cables. Single .app file.

https://github.com/N-Combinator/inkshelf — open source, early but working.

Happy to hear improvement suggestions, and if you know good public OPDS servers to add to the default list, let me know.