NasNas is a lightweight modular 2D game framework with a focus on pixel art style games. It is entirely written in modern C++17, and doesn't have any dependency other than SFML2. It provides a clean and easy to use API.
Allegro Alternatives
Allegro is described as '4 and Allegro 5 are cross-platform, libraries mainly aimed at video game and multimedia programming. They handle common, low-level tasks such as creating windows, accepting user input, loading data, drawing images, playing sounds, etc' and is a game development tool in the development category. There are more than 25 alternatives to Allegro for a variety of platforms, including Windows, Linux, Mac, Android and iPad apps. The best Allegro alternative is Godot Engine, which is both free and Open Source. Other great apps like Allegro are OpenGL, Vulkan, Redot Engine and microStudio.