FPL base is described as 'low level C++ game library developed by Google. It is open source and can be extended by the user or by adding other libraries in the FPL suite: Corgi,Mathfu,Motive,Pindrop,FlatUI and Flatbuffers' and is a Game Development Tool in the Development category. There are six alternatives to FPL base for a variety of platforms, including Windows, Linux, Mac, Windows Phone and Haiku. The best alternative is Godot Engine, which is both free and Open Source. Other great apps like FPL base are Wicked Engine (Free, Open Source), Rogue Engine (Free), Bevy Game Engine (Free, Open Source) and Limon Engine (Free, Open Source).
Godot is a fully featured, open source, MIT licensed game engine. It focuses on having great tools, and a visual oriented workflow that can export to PC, Mobile and Web platforms. It is a cross-platform 2D and 3D game engine and game development IDE.
A refreshingly simple data-driven game engine built in Rust. Free and Open Source Forever! Data Driven All engine and game logic uses Bevy ECS, a custom Entity Component System - Fast: Massively Parallel and Cache-Friendly.
A game-engine fully integrated in Blender UPBGE is an open-source, 3D game engine forked from the old Blender Game Engine and deployed with Blender itself. This unified workflow is its main strength, as you can make your game from start to finish without leaving Blender.