In our spare time, my friend Mars and I run a tabletop RPG over the internet between the two of us called MONAD.
While taking cues from D&D, the majority the game was created from scratch--we designed the character creation, leveling, class, combat, and narrative systems, all unique from D&D and other roleplaying games. We've been running it since 2015, and it's currently around 700k words total.
I've created several small narrative games for it, the best of which is linked here or from the left image.
One of the key differences between Monad and D&D is the way players interact with the game. We wanted to switch player characters throughout the story to toy with different viewpoints and gameplay styles, and some of these parties are bigger than others, so at any given moment one of us could be controlling anywhere from one to five characters at once. For combat to move at a reasonable pace, we had to simplify it compared to other RPGs, so characters usually only make one or two rolls per turn. Strategy is found mostly in team composition, and how characters' abilities bring out strengths or weaknesses in others.
This also highlights the best part of Monad: unlimited customization. Since it is a system we make ourselves, we often create entirely new classes and abilities on the fly. Many of these classes are completely unique and don't show up in other characters, so rather than pasting our character on top of an existing class that many not offer the options that would best suit their personality or story, we craft classes around the characters. Another great benefit is this also allows us to tweak balance while playing if the balance is off. The game is a constant cycle of creative iteration.
Below are some character sheets.
While the RP isn't something either of us plan to produce professionally, both Mars and I make use of the RP as testing grounds for ideas we've used in our professional work. A lot of my projects have started as ideas from the RP (for example, one of the other games on my portfolio, Rivium, is an RP game.) It has had a profound effect on the way I design and balance stat-driven character systems, as well as vastly improved my ability to design and write characters.