Godot does not seem to be for you? Maybe give those projects a look
In light of the recent unity controversy lot of devs have been searching for their new home, and while Godot seems to be considered the goto by majority of the community some of you may find it lacking critical features for your projects/workflow. If that's the case, maybe take a look at this short list of free (as in beer and speech) and open projects which might spark your interest.
3D:
Defold
Defold was originally internal engine of King studio (Candy Crush etc.), eventually made available for general public and later moved over to the Defold Foundation and open-sourced under Apache 2.0.
It provides an IDE, although some of the tooling is a bit spartan, lightweight 2d and 3d renderers, extensions to allow various forms of monetization, a decent UI framework called druid, and access to its own asset store. It uses Lua as its main scripting language, emphasizes composition and while the engine is technically extensible with c++, your mileage may vary. As for the platforms it allows you to target all the major consoles, Windows, Mac, Linux, Android, iOS and web.
In my opinion, it is one of the options closer to unity (although it's 3d renderer is very lacking compared to that of unity).
O3DE
After Amazon bought out Crytek, they took bunch of the Cryengine tech and turned it into Lumberyard, both Lumberyard, and its renderer Atom got eventually open-sourced under the O3DE project with Apache 2.0.
The engine provides complete IDE and is incredibly resource hungry during debugging/development, it also provides you access to extensive library of modules. It uses Lua as its main scripting language and as is extensible through python and c++. It allows you to target Windows, Linux, Android with experimental support for Mac and iOS.
HeapsIO
Originally developed at Motion-Twin (Dead Cells) later inherited by Shiro (Darksburg, Northgard, Wartales) and open-sourced under MIT license.
The engine was originally designed without IDE, but eventually HIDE got developed, it's still pretty bare-bones, although it provides pretty nice integration with some of the other Shiro tools such as CastleDB. HeapsIO uses was written almost entirely in Haxe and uses it as it's main scripting language. It allows compilation for almost all major platforms.
Stride3d
Originally developed under the name Xenko by Silicon Studio (Bravely Default) later open-sourced under MIT license and renamed to Stride3d.
The engine comes with a very mature IDE. It was written primarily in C# and uses it as its scripting language. It allows you to target Windows, Linux, Android, iOS and Xbox.
It feels very close to unity in terms of both the IDE and its C# API.
Rebel Fork
Rebel Fork is a more actively maintained fork of Urho3D, distributed under MIT license.
The engine comes with a very bare-bones IDE, and I would not expect it to get much better since the maintainers and contributors clearly state that the UX of the editor is low priority. It was written primarily in c++ and uses it as its primary scripting language, while it does provide C# bindings they are still in very early stages of development. It allows you to target Windows, Linux, Android, Mack, iOS, Xbox and Web.
Torque3D
Torque was first developed by Dynamix (Tribes, Tribes 2) in early 2000s, later acquired by GarageGames and open-sourced under MIT license.
While the workflow is slightly different from most other popular engines, it comes with a nice set of GUI tools for both 2d and 3d. It was written primarily in c++ and uses TorqueScript (simplified c++) as its primary scripting language. It targets Windows, Mac, Linux.
bevy
Bevy is a community driven engine released under MIT license.
It is code centric and does not provide any IDE. It comes with both 2d and 3d renderers and is centered around data oriented ECS. It was written primarily in rust and uses it as its primary scripting language. It can target Windows, Mac, Linux, Web, iOS and currently developing Android support.
raylib
Raylib is an open-source lightweight framework with zlib license.
It provides no GUI. And you have to compile it yourself. It comes with 2d and basic 3d renderer (unfortunately without proper gpu acceleration, so the you might run into some bottle when trying more complex 3d visuals) . It was written in C99 and supports it natively, it also has bindings for about 60 languages, be it the popular ones like C#, Go, Lua, Kotlin, Ruby, JS or Python. If you want to get your grandma into game programming, its FORTRAN and Lisp (COBOL binding is unfortunately out of date) bindings make it an ideal choice :). It can target any platform supporting OpenGL and C99.
libGDX
libGDX is an open-source framework with Apache-2.0 license.
It provides no GUI outside of a basic tool to setup projects, although there are some community made editor tools and integrations. It uses primarily java, but dedicated Kotlin binding is available. It can target Windows, Linux, macOS, Android, web and iOS.
2D:
LÖVE2d
LÖVE is a simple minimalist framework for making 2d games licensed under zlib license.
It provides no IDE. There is a variety of libraries for it, for example lovetoys for ECS, quickie for UI. It uses Lua and runs on Windows, Mac, Linux, Android and iOS.
HaxeFlixel
HaxeFlixel started as an open-source haxe implementation of Flixel framework, eventually surpassing the original. It is available under MIT license.
It was written primarily in haxe and uses it as its scripting language. It allows you to target Windows, Linux, macOS, Android, iOS, html5 and flash.
FNA
It is an open-source reimplementation of Microsoft XNA framework. It is released under Microsoft Public License.
It provides no IDE. It is primarily 2d but provides some very basic 3d functionality. It uses primarily C# and can be ported to Windows, Mac, Linux, iOS, tvOS, Xbox and Nintendo Switch.
MonoGame
Much like FNA, it started as XNA reimplementation. It is also released under Microsoft Public License.
The main difference between MonoGame and FNA is more frequent updates and asset management, where MonoGame also provides its own GUI tool. It uses primarily C# and can be ported to Windows, Mac, Linux, iOS, Android, PlayStation, Xbox, and Nintendo Switch.
Phaser
Phaser is a framework for web games distributed under MIT license.
It provides no IDE. It uses JavaScript as its primary scripting language and provides TypeScript support. It is purely web game engine.
If you know of any other game engines, please share them, thanks for reading.
Personally, I do not care how far they backpedal this. I do not care if I never make a cent in Unity and never reach their revenue thresholds. I do not care how much time I have sunk into this engine.
I now view Unity, its CEO, and the slew of glorified malware company executives that bought their way onto Unity's board as existential threats to game development as an art form.
Unity has declared itself an enemy to the future of the industry.