Launcher
A small program for your game folder. It keeps the realm's files in step with the server, starts the game, and sends your logs to the admins when something goes wrong. It doesn't touch your Battle.net gateways: the gateway file does that, once.
Using it
1. Put it in your game folder, the one with Diablo II.exe and Game.exe in it, and run it. If it's somewhere else, it asks where the game is.
2. The first time, it downloads what your install lacks. After that only what changed: when the admins push a new release, it comes down the next time you start the launcher.
3. Press Play. The first time, it tells you the game doesn't know Dev realm yet: press Get the gateway file, open what your browser brings down, and say yes when Windows asks. You only do this once.
4. Press Play again. It starts Diablo II.exe -3dfx -skiptobnet. If the game has another gateway selected, the launcher says so: pick Dev realm with the gateway button under Battle.net on the game's main menu.
5. If the game crashes or acts up, press Send logs. You see what goes before it goes, and you get a private link to give the admins.