Once upon a time (actually it was 2010), we thought it was cool to develop a 3D engine, just to get to know how 3D worlds are rendered. The engine was called 'DE Engine' (Dutch for 'The Engine') but never saw any daylight in a product.
Little did we know, but as we dived into DirectX and C++, we got it working. We were able to render Quake 3 maps and hover through them with mouse and keyboard. See the screenshots below for the result.