When comparing GDevelop vs Modd.io, the Slant community recommends GDevelop for most people. In the question“What are the best 2D game engines?” GDevelop is ranked 2nd while Modd.io is ranked 94th. The most important reason people chose GDevelop is:
The whole interface is intuitive and easy to learn: each part of the game can be designed using visual editors. The objects editor is used to create the objects of the game, the scene editor help you to build the levels of your game and the events editor allows to give life to the whole game without programming.
Specs
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Pros
Pro Easy to use
The whole interface is intuitive and easy to learn: each part of the game can be designed using visual editors. The objects editor is used to create the objects of the game, the scene editor help you to build the levels of your game and the events editor allows to give life to the whole game without programming.

Pro Free and open-source
GDevelop's runtime libraries are MIT licensed. It can be used freely for projects of any type and there are no royalties associated with publishing games developed with GDevelop.
Pro Powerful events system to create games without programming
No need for coding using this system which is clear and powerful: events are composed of conditions and actions. Actions are launched when conditions are fulfilled.
This is a very friendly way of making games and is still efficient for advanced usage, contrary to most other "block"/"drag'n'drop" systems.
Pro Open source plugin SDK
The plugin SDK is open source, so if you want to extend it, you can.
Pro Lots of features to build games
The engine includes pathfinding, physics engine, multitouch support, custom hitboxes, platformer engine, tiled maps, multiple layers and cameras out of the box.
All of these features can be used without programming knowledge, using the visual editors.
Pro Quickly add behaviors to objects
Prebuilt behaviors can be added to objects. This is a very efficient way to add a physics engine or make a platformer game. Lots of behaviors are included, from the most advanced (Physics, platformer, top-down movement) to really simple one (like the behavior to destroy objects when outside the screen or the one to drag objects with mouse or touch).
And you still have full controls over your game as behaviors can be modified using the events!
Pro New documentation for gd5 is good for starting
A new doc is improving for gd5 that is nice for beginners and after that you can learn more from examples. Also, gd4 wiki is still there.
Pro Constant updates
New releases and bug fixes are consistent. New updates are released anywhere within 2 weeks or 1 month from the last one. Its auto-updater also does it job very well making life a lot easier.
Pro Online version available, compatible with iOS and Android
Thanks to its open source nature, GDevelop-App.com was built over the GDevelop engine.
GDevelop-App.com is a complete game creator similar to GDevelop, available directly in your browser and compatible with iPad and most Android tablets and phone! The app is perfect for making games directly from your sofa and you can even start a game on GDevelop-App and export it to open it inside GDevelop.
Pro Multilanguage support
GDevelop is available in many languages and even community can help in translations.
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 No support for atlas/tilemap and sprite sheet
At this point, you need to separate the tileset maps or character animation sprite sheet before importing it to the engine, but the developers are working on this feature.
Con GUI is slow to load
This makes doing the simplest things, like looking at one of your maps, hard to do. In looking into this program, it can stall a PC while trying to load a sample map.
Con No 3d, not even fake 3d
This is a 100$ 2d-only game engine. You could of course use pre-rendered 3d graphics, but your games themselves will exist only in the x and y axes.
Con It's very slow
Although suggested otherwise, GDevelop doesn't compile the games - it just adds wrappers so each OS can run the HTML5 game it creates. That means it runs much, much slower than other engines that do compile games.
Con No cross-compiler
The Windows and Linux versions of GDevelop can each compile a native application; but the Windows version cannot compile for Linux, nor vice versa.
Con Optional subscription not mentioned on main site
While the engine is free and open source as stated on the main website, it does not mention that some optional features and services are actually activated through a paid subscription (two tiers: 2€ and 7€). Those features are: no nag screen shown when debugging, additional metrics available on games dashboard, access to more than 2 cloud exports per day (unlimited local export can be done without subscription, provided the right packaging tools are installed and configured), easy removal of GDevelop splash screen (can be done manually without subscription).
Con Behaviors of Objects are rather generalized
Since it has a fully GUI editor, the objects you are allowed to add in your game are pretty generalized (PhysicsObject, TiledSprite, PlatformerObject, etc). This limits the freedom of a game developer while making a game, as the object msut follow the preset behaviours imposed on it.
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.
