Installing OpenTabletDriver

Install OpenTabletDriver, it's daemon and GUI by:

/etc/nixos/configuration.nix

{ config, lib, pkgs, ... }:
{
  ...
  # Enable OpenTabletDriver
  hardware.opentabletdriver.enable = true;
  ...
}

Troubleshooting

Check out the official OpenTabletDriver Wiki

Warning: Do not run otd-daemon as root

But in case you do, run:

sudo rm /tmp/CoreFxPipe_OpenTabletDriver.Daemon

to stop the daemon from crashing when ran as user again.