What is the best way to write, or where to get an engine for 2D (2.5D) MMORPG?

Question

Programming

The bottom line is, you need a 2D engine for an RPG game. If there is an absolutely free and independent engine that satisfies the requirements described below, then where to get it, if not, then what is the best way to write it, and what is needed (what programming languages)
Important features:
*Real-time - real-time gameplay, (T. e. NOT turn-based, of course)
* Open world - ie. the ability to create a large polygon, without seams.
*Multi-storey.
*The ability to put the game on this engine on the server rails, ie. online . (It is desirable to make it client-side or browser-based)
Appearance is something like this:

Answer 1

Unity3d will be a great start for you. Unity is the most powerful platform on which you can do anything. Including 2d MMO.
But it will not be easy, I warn you right away. You can make a platformer or a 2D rpg on a unit very quickly, but making an MMO is a much more difficult task.
(Unity3d 5 is currently developing a new platform for networking, and there they promise to greatly simplify networking, including in MMO projects).
There are some difficulties with seamlessness, but they are solved. Unity already has a huge functionality that covers all the basic requirements for any game, plus there is an extensive store of addons (assets).
Any platform - and the client, and the browser, and mobile phones, and even consoles.
The programming language is the main C#, you can write in Javascript (more precisely, a language very similar to javascipt) and Boo (something like Python).