Most fighters learn to use the Martial weapons to a profience extent and combine it with there other powerful prowesses. However certain fighters have chosen to master a select few weapons to master and learn the ins and outs of, becoming martial masters.

So this is a fighter subclass idea I thought about recently combining some interesting ideas, the two main prowesses being 

1. Selecting certain mastery weapons that your character has mastered
2. Using those weapons to a greater extent like using a mace to stun someone, a whip to restrain someone from afair, or even use a net more effectively, also maybe some other simple bonuses like adding profiency to damage with these mastered weapons or stuff like that
3. Trading attacks to use abilties, like maybe trading 2 mace attacks to do a stunning mace strike, it could work like battle master selecting or maybe judt getting a set few at level bonuses depending on what your mastered weapons are

These are just some ideas I had and I'd like to hear what others think about them

Sounds like you're wanting a homebrew similar to one I saw while back... It's all about dual wielding weapons in order to gain additional effects. Master-At-Arms

 I also wanted to take a bit of inspiration from a subclass I found called warlord, which had a trade attacks for special command moves, except now instead of command moves different weapons