When comparing Gideros vs GDevApp, the Slant community recommends Gideros for most people. In the question“What are the best 2D game engines?” Gideros is ranked 26th while GDevApp is ranked 83rd. The most important reason people chose Gideros is:
Gideros provides on device players for iOS and Android that can be used to instantly try out your code directly from the Gideros IDE.
Specs
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Pros
Pro Instant on device testing
Gideros provides on device players for iOS and Android that can be used to instantly try out your code directly from the Gideros IDE.
Pro Auto scaling and image resolutions
Gideros provides an easy way to target various screen sizes by providing automatic scaling options and choosing the best image resolution based on device screen automatically
Pro Local builds
You can build apps without an online dependency.
Pro Friendly & helpful community
Gideros has an active forum where you can find friendly and helpful advice.
Pro New features and improvements are released regularly
Gideros is being constantly updated and improved by the main developers.
Pro All in one studio, no complicated setup
Gideros Studio is incredibly easy to set up. Once installed it is very easy to create a new project or open one of the many example projects. Trying out an example on the desktop is two clicks away.
Pro Easy plugin architecture
Gideros Studio has a very powerful feature which enables developers to use a C/C++/Java/ObjC library next to Lua. This way it's possible to call the library functions under Lua, get the results and interpret them directly under Gideros Studio.
Pro Supports many platforms
Gideros supports iOS, Android, Windows, MacOS, WindowsRT, Windows Phone and HTML5 platforms.
Pro Amazing 2D performance
2D performance is amazing.
Pro Very easy to learn
Gideros uses the Lua programming language which is very easy to learn (and very powerful). There are some excellent video tutorials too, to help you get started. The Gideros forum community are also very friendly and helpful if you any any problems.
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 ones (like the behavior to destroy objects when outside the screen or the one to drag objects with mouse or touch).
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 beginner-friendly way of making games and is still efficient for advanced usage, contrary to most other "block"/"drag'n'drop" systems.
Pro Intuitive interface
Pro Based on GDevelop
The entire webapp is based on GDevelop, an open source native game development software available for Windows & Linux, so it benefits from its advanced development.

Pro Can download an archive of the game source
Even though the tool depends on having a server up and running, you can download a copy of your game to run locally, or host somewhere else.
Pro Great UI
Sleek and user-friendly UI.
Pro Can export your game as HTML5 and for Android
Games can be packaged for Android without relying on any third party tool. You can also export your game and download it to host it on your server or let it be hosted on GDevApp.com.
Pro Shallow learning curve
Cons
Con Few resources, but growing
Gideros has a small community, and therefore do not have as many "How to make a game" tutorials. However, there are a couple of excellent books available that can take you through the fundamentals.
Con The Gideros IDE is not as fully featured as other IDEs
The Gideros IDE is not as fully featured as other IDEs, but you can easily use the very powerful and compatible ZeroBrane Studio IDE.

Con Depends on a hosting service
If the website goes down or closes down, you'll no longer be able to develop your games using this system (but you can download a backup of your game from time to time and open it with GDevelop).
Con Cannot deploy native games
For now, games developed with GDevApp can only be deployed for the Web. Android deployment is in the works, but even then, they won't be native since they are built with web technologies.
