I somehow stumbled on Polycode, which is an interesting "free open-source framework for creating crossplatform games and interactive applications". It reminds me a bit of Processing, except that you use C++ or Lua for creating applications.
In addition to supporting 2D and 3D applications, it features a large selection of asset loaders (including Blender, of course) and has a Unity-like IDE. Runs on all major platforms, though there are no ready-to-download executables yet. You'll have to build everything from source to get started.
As an added bonus, there is a blog linked to the polycode. Always nice to see developers writing about their pet project.