Have you ever invented a new and unique game (or strange twist on an old game)

Well I designed a browser MMORPG but I haven’t gotten it working yet :(

You mean like creating house rules for an established game? Yeah, my college friends and I played our own variant of Uno, called Mortal Kombat Uno. It was the same as the regular game, with four rule additions:
1) Draw Until You Can Play: If you can’t play a card, rather than drawing one card and then either playing or passing, you must continue to draw cards until you draw a card that can be played.
2) Stacking: If someone plays a Draw Two on you, and you have a Draw Two in your hand, rather than drawing 2 cards, you can play your Draw Two. Then the next person must draw 4 cards – unless they also have a Draw Two, in which case they can play it. And that continues until someone can’t play a Draw Two, and that person must draw 2 cards per Draw Two that was played up to them. The same rule applies for Draw Four Wild Cards.
3) Feeding: If someone leaves the table (to use the bathroom, get a drink, answer the phone, etc), the game is not paused. Instead. when it is their turn, they are given (“fed”) two cards and then skipped.
4) Mortal Kombat: When you have an identical copy of the card most recently played, you may play that card, regardless of whose turn it is. You must play your card before the active player is able to play their own card. Play then continues on from you. This can also work in conjunction with the Stacking rule as described above.

Scrabble, but you can only use proper pronouns (and you have to be able to prove that it actually existed before the game, usually via Google, though other sources are taken).

I babysat a kid who was home from school sick last week, so we played a lot of games. After a while we realized we kept coming back to Pick Up Sticks and Sorry!, so we combined them. Before I (with the red pawns) could take a turn in Sorry, I had to earn it by successfully picking up a red stick from the pile of Pick Up Sticks, e.g. Hours of fun!

When we, my 2 brothers & I, were kids we’d compete in our own special indoor olympics.
This would usually take place on miserable cold rainy days, being “penned in” can cause madness.
We would “swim” across the living room floor, trampoline on the beds & hurdle over chairs.
Lot of fun as it happens.

When I was a kid me and my friends invented a complex hide-and-capture game. Similar to capture-the-flag, but with a ball and a lot of complex rules that I don’t totally remember any more.

Our house was on a lot of land and there would sometimes be over a dozen kids here playing this game. Sometimes it was kids that I didn’t even know.

We used to play cops and robbers on bicycles in the streets of our home town in the summer months. I don’t remember the rules so clearly but it was fun. The streets are too busy nowadays.

My little brother and me told each other words that started with the last letter of the previous word and after that we had to say them again in the opposite direction (he had to say my words then and I had to say his).
The goal was to brake the record of the amount of words we succeeded to say (forth and back).
We were about twelve-thirteen years old.