From 1.17 onward this is only required Server Side. However, in 1.18 and beyond it is nonetheless recommended to install client side to fix visual errors.

Allows 2 players to ride one horse! 

Horses have the same behavior boats, so the front player gets to steer while the back player gets a free ride!

Very easy to use, just tame a horse and have your friend right click after you hop on!

Q: I love this awesome mod, Flytre! When is it coming for forge?
A: I just became a blacksmith in 1.18.2. If you need versions prior to then, check here.