https://www.google.com/search?q=mmorpg+authentication&ie=utf-8&oe=utf-8
https://forum.unity.com/threads/mmo-trying-to-get-the-hang-of-how-an-auth-server-works.13653/
https://forum.unity.com/threads/mmo-login-server-question.382240/
https://www.gamedev.net/forums/topic/566478-login-server-for-mmo/
https://www.reddit.com/r/gamedev/comments/697sjm/mmo_load_balancing/
https://forums.mmorpg.com/discussion/409785/what-would-a-good-mmorpg-authentication-system-look-like
https://www.eveonline.com/article/building-a-balanced-universe
http://ithare.com/chapter-via-server-side-mmo-architecture-naive-and-classical-deployment-architectures/

[C#]2D MMORPG Tutorial - EP0: GETTING STARTED https://www.youtube.com/watch?v=vXRlB4ruPu8
Unity 3D Tutorial #1: MMORPG | Creating our own Server Network https://www.youtube.com/watch?v=1wlCk8xSBi8

Databases

http://www.vertabelo.com/blog/technical-articles/mmo-games-and-database-design

https://www.binpress.com/tutorial/creating-a-city-building-game-with-sfml/137
https://scottlilly.com/learn-c-by-building-a-simple-rpg-index/
https://scottlilly.com/build-a-cwpf-rpg/
https://meruvia.fr/index.php/programmation/18-big-tuto-c-sfml-2-action-rpg

Lets Build A MMORPG - Part 1 Game Maker NodeJS
MMO Phaser Express Socket](http://apprendre-le-js.com/mmo-phaser-express-socket-par-1/) French
Building a Multiplayer Game with HTML5(Impact Engine) and Node WebSockets Part 1
Building an MMO by Yourself | Robby ZINCHAK
http://gameprogrammingpatterns.com/contents.html
https://assetstore.unity.com/packages/templates/systems/ummorpg-51212

Open source projects

Planeshift
Worldforge
The Mana World

http://journal.stuffwithstuff.com/2014/07/05/dropping-loot/
https://dvnc.tech/2018/05/10/ultimate-guide-to-getting-started-in-game-development-with-100-resources

Architecture

https://www.ibm.com/developerworks/library/ar-powerup1/index.html