When comparing Moai SDK vs Modd.io, the Slant community recommends Moai SDK for most people. In the question“What are the best 2D game engines?” Moai SDK is ranked 19th while Modd.io is ranked 94th. The most important reason people chose Moai SDK is:
Because it uses Lua + C++.
Specs
Ranked in these QuestionsQuestion Ranking
Pros
Pro Fast
Because it uses Lua + C++.
Pro Gives you total control
You can use your own custom shaders and extend the language with C++. MOAI doesn't give you everything, instead it gives you the tools you need to develop any game you want.
Pro Full source code is available
So it is extendable with C++
Pro Easy-to-use particle engine
Uses a limited subset of Lua
Pro Uses Lua, with LuaJIT where possible

Pro Is used by many pro developers
Moai SDK is used by popular developers including Double Fine for their mobile game, Middle Manager of Justice, and for their Kickstarter hit, Broken Age(formerly, Double Fine Adventure.) It was also used to create the popular mobile game Bubble Ball 2.
This proves that this engine can be used to make fully-featured and fun games.

Pro API interfaces
Has options for development like Hanappe and Rapanui, providing a different way to interact with the engine.
Pro Helpful community
The Moai SDK Forum is active and users will go to great extents to answer queries, post code snippets, beta test, and even purchase and give feedback on each others' games.
Pro Helpful and detailed documentation
Although the Moai SDK is very advanced and uses complicated features, the documentation wiki thoroughly and clearly explains how to use these features, such as the Moai Cloud(a service that provides web services for your game), and multiple ways to build from source.
Pro Its Fun, its easy to script
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Pro Runs well on low-end devices
The game client doesn't use much CPU nor bandwidth.
Pro Free
By far, this engine is completely free to use.
Pro No installation required - super easy to get started
Modd.io runs in browser, it provides IDE, map editor, and asset manager all in one platform, so you don't need to download or setup anything.
Pro Easy to use free Asset Library
You can easily change your game assets (images, sound, etc) with a single click using modd.io Asset Library
Pro Has multiplayer support baked in
This engine supports up to 64 concurrent players, and hosts servers for you as well
Pro Perfect for Impatient game developers
It literally takes 5 minutes from signup to publishing my game
Pro Easy to use
Modd.io is designed for new/intermediate developers who wants to get into game development. You should be comfortable using the engine after spending about 15 minutes in watching tutorial videos
Cons
Con Not for beginning developers
The Moai SDK has very advanced features which allow it to create powerful games. A drawback from this is that it is not very suitable for beginners.
Con Not necessarily tested or stable

Con Scarce documentation
Since it is a minimalist framework there is not that much documentation, but if you are used to reading API references and source code you are good to go!
Con Development has ceased
The last update was over a year ago. Users should not expect things to still work on future OS versions unless they're ready to fix them yourself.
Con The engine is evolving in a bad way
Over the last updates, many useful features have been removed, making it harder to create more complex games.
Con Not very secure
Modd.io comes with its own security issues. Many of them have been used to destroy eachother's games, which completely busts your progress on your game unless you have backed it up by exporting it's JSON.
Con Not Possible for stuff
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Con Annoying asset size limit
Each asset is limited to 800kb (except for audio being 3mb) which is okay for simple assets but unacceptable for creating spritesheets for animations or tilesheets for the map.
Con Very flat map
No matter how well game maps are made, all of them look just not beautiful.
Con No/limited camera manipulation
You cannot create a shake effect which is also urgently needed in complex game creation.
Con Certain variable datatypes are urgently needed but do not exist.
Such datatypes as arrays composed of numbers, strings, etc are needed to create complex games but just do not exist in this game engine.
Con Joke-y community
Most of the staff team in the community are constantly behaving like jokers. It just always feels like 80% of the staff team is not the right pick for such a community.
Con The homepage is not good
The homepage allows players to join your game, but the way it works is just not good. The "unpopular 0 player" games get less exposure than the popular games. The tier system also puts a star on your game card which also lures players to your game making them think this game has a special event or something, giving a disadvantage to the less popular games which are still so called "Tier 1".
Con Not very powerful
This engine is ready to use right away, but already starts dropping framerate at over 1000 units which are not very active.
Con Tier-based servers with certain lockdowns
Modd.io "tiers" all the games you create. The very basic tier, commonly called "Tier 1" is very limited and removes motivation to develop a game.
Con You'll have to learn a new programming language
This engine has it's own IDE with a drag and drop style programming language. It does take a good 2 hours to get familiar with the API..
Con No lower level API access
You cannot access lower-level APIs through this engine, such as the renderer.
Con No single player support
All games in modd.io must support multi-player game mode.
Con Limited customizability
Modd.io is designed to be good at making "specific" kind of multiplayer games. Its strength unleashes if you don't care too much about the specifics in UI. For example, if you wanted to make a casual death match game, it is extremely easy to make it using modd.io. However, if you want to create a puzzle game with a unique UI, it becomes very time consuming.
Con No 3D support
This engine is limited to 2D only.
