When comparing Leadwerks Game Engine vs GDevApp, the Slant community recommends Leadwerks Game Engine for most people. In the question“What are the best 2D game engines?” Leadwerks Game Engine is ranked 76th while GDevApp is ranked 85th. The most important reason people chose Leadwerks Game Engine is:
Leadwerks's flowgraphs resemble flowcharts where each box represents a function or value, with connections between them representing program flow. This provides a better at-a-glance indication of game logic than a simple list of events, and makes complex behaviors easier to accomplish.
Specs
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Pros

Pro Versatile flow diagram script model
Leadwerks's flowgraphs resemble flowcharts where each box represents a function or value, with connections between them representing program flow. This provides a better at-a-glance indication of game logic than a simple list of events, and makes complex behaviors easier to accomplish.
Pro Built-in level editor
Has an acceptable 3D map editor that is easy to use.
Pro Handful of Prefabs and Scripts
For example, you take a model (e.g. torch), add a light source to it, add a particle generator (for fire) and save it as a prefab (one file). Then this prefab can be used to add many torches with fire and light.
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 Very buggy
Leadworks is a not complete, it's a work in progress. As such many parts of the engine are clunky, especially the level editor.

Con Documentation and support are limited for non-coders
The flowgraph editor can be used with free script assets to build games without writing any code, but this is not directly intended or encouraged by Leadwerks.
Con Highly misleading advertising

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.
