While everyone has a specific type of MMORPG or MMO they like, there are people who also want "Infinite" Possibilities via sandboxing. Only truly way to do this though is to make your own MMORPG yourself via Engines provided all over the Internet. (We also still have yet to see the true potential of the new Unreal Engine 4.) But for those of us not graced with programming knowledge, or don't even know where or how to start (Blender for Modeling?) This thread aims to tell users what there is in Sandbox MMO/RPGs. Currently the list is likely incomplete, or never will be, and people can contribute to the list by replying below this thread opener.

The Problem: Sandbox Versus Game-play
Before we get into the list however, I'd like to take this time to explain and hopefully get you into what you really want in a sandbox MMO. First off, is the overall problem, what would you rather have: Game-play or Sandboxing? Most people would likely counter that with "How about both?" while you CAN have both, it isn't always an ideal situation to have BOTH. For instance, let's say you build a bridge that can be destroyed by anyone or anything, and link it to an NPC that will repair it over time. The bridge would likely be destroyed by trolls, greifers, etc. wanting to make the game much harder than it should be. You could counter this with measures like, "Only Monsters can attack this structure" or "You can help rebuilt this bridge with X amount of X material." Whatever the case, you have to correctly balance game-play and sandbox ability. This often limits how fast a developer or publisher (or both!) can push their game, as it requires so much more coding, variables, structures, animations, and all that. Mostly though, game publishers and developers would rather go to the Game-play side of things, rather than allow users to completely sandbox. This causes the game to be limited in what people can do. Often, you would have to go through a commotion and contact the developer directly to see if they have any say in the matter. Usually they won't reply, or the publisher won't reply (or both!) It's up to you to decide what you really want.

The List:

Salem: Salem
"Paradox Interactive today officially announced Salem, a free-to-play Massively Multiplayer Online (MMO) game based in the harsh world of colonial Salem. The game focuses on crafting and player colonies as players discover the new world in a sandbox like environment. The game is being developed by the team at Seatribe and is scheduled to go live in 2011 on the Paradox Connect platform." -- Paradox Plaza

Linkrealms: Linkrealms - Sandbox MMORPG
"This game is great there is a lot of content for being in a fairly early beta stage. The community of the current beta testers are awesome people they will help you with understanding and playing the game and even show you realms if you ask nicely they will ask any question and basically are your tutorial for the game, the devs even sometime pop in and help out too.

The breeding alone is incredibly complex, no rooster will EVER be the same The genetics of each rooster are varied and can transfer the behavioral patterns and fighting style as well as looks. here the video of it http://www.youtube.com/watch?v=R4HxhH2y2oo I'm sure you will be amazed at what is and can be capable with there style of breeding." -- Bay 12 Forums

Pathfinder Online: https://goblinworks.com/
"Pathfinder Online is a hybrid sandbox/theme park-style MMO where characters explore, develop, find adventure and dominate a wilderness frontier in a land of sword and sorcery. The Pathfinder world is high fantasy in the tradition of epics like The Lord of the Rings, Conan, the Wheel of Time and Game of Thrones."

Minecraft - mcmmo: http://mcmmo.wikia.com/wiki/McMMO_Wiki
"McMMO is an open source plugin for the Minecraft multiplayer server mod Bukkit that is currently under development by Nossr50. This plugin allows for an RPG-like experience to exist in the world of Minecraft complete with experience points, special powers, parties, PvP and more!"

Perpetuum Online: http://www.perpetuum-online.com/
"In the not-too-distant future, a strange anomaly opens the gates of the universe for humans. With this new technology, energy, information and atomic size objects can be transported to anywhere in space. The most intriguing of all new discoveries is an Earth-like planet, where humanity discovers a new source of energy, vital to its unbroken advancement. However, this planet is inhabited by a synthetic, robot-like life form. Their technology and resources are the goal of humanity's new conquest. Players may take part in various areas of the project. They may fight on the front lines for new territories, develop the already established infrastructure, trade goods or services, or even set their own goals and set up their own corporations." -- Perpetuum - What is Perpetuum?

Heaven & Hearth: http://www.havenandhearth.com
"Haven & Hearth is a MMORPG (Massive Multiplayer Online Roleplaying Game) set in a fictional world loosely inspired by Slavic and Germanic myth and legend. The game sets itself apart from other games in the genre in its aim to provide players with an interactive, affectable and mutable game world, which can be permanently and fundamentally changed and affected through actions undertaken by the players. Our fundamental goal with Haven & Hearth is to create a game in which player choices have permanent and/or lasting effects and, thus, providing said players with a meaningful and fun gaming experience."

Wurm Online: http://wurmonline.com/
"Wurm Online is a 3D Massively multiplayer online role-playing game that was originally produced by Mojang AB in Stockholm,Sweden. Development started in 2003 by friends Markus Persson and Rolf Jannson, and it was released for personal computer's in 2006. Players can choose to play on servers that allow player versus player combat and realm versus realm combat or servers that are focused more on a virtual economy." -- Wikipedia

Terraria: http://www.terraria.org/ *
"Grab your tools and go! You can do many things in Terraria: make weapons and fight off a variety of enemies in numerous biomes, dig deep underground to find accessories, money, and other useful things, gather wood, stone, ores, and other resources to create everything you need to make the world your own and defend it. Build a house, a fort, even a castle, and people will move in to live there and perhaps even sell you different wares to assist you on your journey. But beware, there are even more challenges awaiting you... Are you up to the task?"

Garry's Mod: http://garrysmod.com/ *
"Garry's Mod (officially abbreviated as GMod) is a sandbox physics game using the Source engine. Garry's Mod has been available on Valve's content delivery service, Steam, since November 29, 2006. Despite being a standalone game, Garry's Mod requires the user to own at least one game on Steam based on the Source engine, such as Half-Life 2, Counter-Strike: Source, Portal, or Team Fortress 2." -- Wikipedia

EVE Online: http://www.eveonline.com
"Your actions in the Sandbox can lead to the destruction of starships, the creation of a thriving corporation or the doom of an empire. Every action taken by every player affects the state of the Sandbox, and through it those actions affect every other player. The web of action and reaction in EVE leads to emergent gameplay where a single shot, business deal or even just a word can determine the destiny of thousands." -- EVE Online - Sandbox Page

* Note: As of now, I know of no "Dedicated Servers" for these.

News Sites:

Sandboxer.org | Sandbox MMO News