This is a screencapture of a game engine I have been developing with Game Maker 6.1 for over 5 years. The earliest screenshot I have is far simpler and more crude than this and is from 2011.

The engine supports the following:
-Polygon-based level background and foreground (WIP) rendering, which liberates the game from being stuck on a grid-based tile set (tiles can still be used where required). This results in reduced file size.
-A character movement system which can be used with the above to allow characters to be a part of the landscape you create (WIP)
-Lighting with a full day/night cycle and shadows
-A single water surface is permitted per level, featuring reflections which could be made configurable in the future
-Character animation system capable of supporting many states (hanging off/climbing ledges, kneeling and crawling etc.).
-Flexible, fully integrated character equipment system which would support many character types/species, allows parenting at different depths, and is significantly more in-depth than your standard "choose a torso/legs/arm/helmet piece", allowing any number of clothing and/or armour layers. Furthermore, character customisation can be supported using this system, providing complete integration with the character animation system and giving your players as many options as you may wish to provide.
-A generic, entirely custom window-based user interface which is currently, visually only implemented for the previously mentioned system. Windows consist of a complex arrangement of polygons, allowing windows to be resized and reduced to icons.
-An editor for level backgrounds with full saving and loading, which supports numerous types of polygons
-WIP: A simple audio effects system making use of DirectSound's plugins to alter sounds like footsteps, wind etc. in real-time. This saves from having to use countless .wav files for different environments which would bloat file size. This could also be adapted to smoothly change the properties of reverb and other effects between different locations (e.g.; moving from indoor to outdoor).

All of this was originally developed on my 2006 Dell Inspiron 640m which I have kept on life support for several years, though I am now moving development to a VMWare virtual machine running Windows XP mode. I am using such an old version of Game Maker that Windows Vista and later do not support the executables created by Game Maker 6.1 and I must run them through a converter.

All art is created by me right down to the font used for the debug values, and all programming was done by me, no external libraries were used.
As this is developed using Game Maker 6.1, no shaders have been used for development.

Trello board:
https://trello.com/b/mSBP3HO6/2d-pl.....pg-game-engine