Verisimilar let's you create custom quests, NPCs, or modify existing ones. RP use only.

Introduction
Have you ever wanted to run an adventure in WoW, like you did when playing Dungeons and Dragons, or any other tabletop game? You can do it in the game, but you have to make a lot of compromises. You could pretend to be an NPC using your characters, but the players would still see that they interact with their old buddy.

Verisimilar helps you create that sense of immersion that's sometimes hard to achieve when running your own storylines. It allows the Game Master (GM, and when used in the context of the add-on it does not mean the Blizzard GMs, but the player running their own storylines) to enhance the players' game world, by modifying already existing assets, creating new ones, and interacting with the players through them.

Other than storylines, you can also use it for other occasions that could benefit from a little world enhancing. For example, if you are running a tavern, you could give your NPC bartender more gossip options to develop his personality, or even converse with the customers through him. Or a leader of a military guild could give out that day's duties as custom quests.

Right now, the only assets a GM can modify or create, are NPCs and quests. In the future, you will be able to add new items, books, and create custom loot tables for monsters, among other things.
Legality and Limits
This add-on is completely legal in accordance with the Blizzard add-on policy. It does not add or modify game assets found in the .mpq files. That also means that there are a lot of limitations to what it can do. You cannot, for example, add the 3D model of a character to the game world, much less be able to fight it.

You can, however, affect most of his interaction with the game world that happens through the user interface.
Verisimilar and other Add-ons
Unfortunately, due to the nature of Verisimilar, it does not function well when there are other add-ons present that try to modify or affect the same assets. For example, it will not work with any custom quest log add-ons (like Quest Guru, for example, but it WILL work with QuestHelper). Also, while working seemingly fine, SpamSentry will block the NPC speech, even if you have that option disabled in the add-on. However, you can disable Verisimilar's ability to merge with the interface (and conflict with other add-ons) through it's options page. This, however, will result in a sub-par experience for you, as it will try to interact with the player through other, less verisimilar ways. I suggest that you give it a chance though, and try it with the other add-ons disabled at least once.
The Verisimilar Suite
This is actually a two-part add-on. The zip you downloaded contains the Verisimilar Player and Verisimilar GM add-ons.

Verisimilar Player is what normal players will use. It is what affects their interface and brings the GMs vision to life.

Verisimilar GM is the toolbox that the GM uses to construct and orchestrate his world.

You will find detailed guides for both add-ons in their respective folders

Made by Erethas (Moonglade EU)

Patch notes for Verisimilar
v0.04
-(VGM)Wizards: A new, easier way to create elements.
-(VGM)Added a warning for local sessions. This will hopefully reduce user paranoia by aproximately 87.4%
-(VGM)Selecting quest givers (and enders) for a quest, as well as previous and next quests in the chain, is done by chosing an entry from a list.
-Session version is now indepedant of add-on version. That means that you won't have to ask everyone to update whenever I fix an interface bug.
-(VGM)You can now create macros for your session elements.

v0.03
-(VGM)New NPCs will have the name of the unit you are targeting, making it even easier to create one.
-There is some sort of localization now. Zone names will appear localized. Demo Session still won't work in non-english clients.
-(VGM)Nice new dropdown menu for switching between sessions from every panel.
-(VGM)You can now create your custom scripts in the scripts panel.
-(VPL)Verisimilar now works with Quest Helper! Apparently it was an easily avoidable error on my part.

v0.02
-(VGM)New NPCs will have their coordinates set as the GM's current position (instead of the useless 0,0). Also, their zone will be your current zone.
-(VPL)Fixed bug where Verisimilar would throw an error when closing the gossip window of an NPC when you had unconnected sessions in your list.
-(VPL)Updating quest objectives (killing mobs etc) will no longer add additional copies of the quest to the quest tracker.
-(VGM)A player who is lower than 80 level will no longer be spammed whenever he gains experience through kills. Sorry about that!
-Pop-up menus will no longer linger on the screen when they are out of context (when the window hides or when changing panels)
-(VGM)There is only one Ashenvale, actualy. The impostor has been exposed and purged.
-(VGM)The remove option for a player's active quest is now under it's submenu, instead of between quests.
-Verisimilar now uses Blizzard's pop-up dialog system instead of my own hackish approach. I guess it's better.
-(VGM)Check the new Script Guide in the VerisimilarGM folder!

Still no localization. Sorry!

Verisimilar, archived on 05/10/09
Verisimilar, archived on 10/10/09
Verisimilar, archived on 02/11/09