MonoGame
An open-source .NET game framework continuing the XNA-style API with a content pipeline and multiple platform backends.
Why use it
It is more transparent than an editor-led engine and suits code-focused teams willing to build architecture and tools.
Where it fits
Find engines, frameworks, code libraries, version control, and production automation.
What to check
Editors, scenes, and many higher-level systems must be selected or built, increasing early engineering cost.