Check out some of these sites for more info about NeXT and all things related.
NeXTComputers.org - NeXT file archive and forums, active community of NeXT enthusiasts. Lots of info about older hardware, software, and some modern projects.
Previous - m68k NeXT emulator, check the NeXTComputers forums for more current info.
USB NeXT keyboard with Arduino Micro - Build your own adapter to use a NeXT keyboard via USB! Try it with a Trinket M0 rather than a Micro for native USB.
Drakware - Vintage enthusiast (and author of this guide) building modern adapters and parts for old systems including NeXT. Check out NeXT2USB for an easy way to use a NeXT keyboard and mouse via USB.
NeXT Non-ADB Keyboard Protocol - My investigation into the keyboard protocol for old NeXT systems. Useful if you're building your own adapter.