esp32-nut: share a USB UPS on your network without a Raspberry Pi

esp32-nut is firmware by Pasquale Cuorpo that turns an ESP32-S3 (Wi-Fi) or an ESP32-P4 board (wired Ethernet, PoE on boards that have it) into a standalone Network UPS Tools (NUT) server. The board talks to a USB UPS over USB Host and shares its data with any NUT client (upsc, upsmon, Home Assistant, PeaNUT, TrueNAS, Synology), up to 8 at once, so a USB-only UPS can warn your network of an outage and shut machines down cleanly without a Pi or PC running 24/7. It also runs UPS tests and commands and changes the settings your UPS allows, from a login-protected web UI. The README warns that the web UI runs over plain HTTP, so use it only on a trusted network. Only UPSes that use the USB HID Power Device Class work. Older serial (Megatec) models don't. Unknown brands fall back to a generic driver, and you can export a USB diagnostics file for the author. APC Back-UPS BX units lock up their USB at intervals (NUT on Linux sees this too); since v1.7.1 the board restarts itself after each lockup. On a generic dual USB-C ESP32-S3 board you solder the USB-OTG pads on the back to enable host mode, power the board from a USB charger on the COM/UART port, and connect the UPS to the USB port through a USB-C OTG adapter. On the Waveshare ESP32-P4-ETH the UPS plugs into the 4-pin USB 2.0 HS header (J3); the README lists P4 chip revision v1.x as tested, v3.1+ as untested and v2.x / v3.0 as unsupported. Install from the browser at maverick1982.github.io/esp32-nut; leave "Erase device" unchecked to keep your settings. A 3D-printable case is on Printables.