Weapons in Dungeons and Dragons 5th Edition have a bit of an identity problem for more experienced players. This is caused by there being very little difference, beyond aesthetics, between different weapon choices, beyond the size of the damage die.

This is absolutely perfect for newer players, as the process of making attacks can be boiled down to two simple dice rolls, which allows them to focus more on their roleplay and characters, and allows them to more easily keep up with combat. Exactly what 5e was designed for.

But more experienced players are left wanting for more. Expansion material for the game has introduced so many new spells and unique feats, but weapons have been almost entirely left untouched since the release of the Player's Handbook.

This document details two systems: Weapon Skills and Weapon Mastery, which are ways of adding a lot of additional depth and meaning to the player's choice of weapon for their character. 

Weapon Skills are unique actions the players can take on their turn, or replacements for normal attacks, that add additional functionality to all weapons. The weapon skills provided by weapons are dependent on whether they are used in one hand, wielded in the off-hand for two-weapon fighting, or if they are wielded in both hands, such as with two-handed weapons or versatile weapons.

Weapon Mastery is a progression system, where players keep track of how well they use a weapon or shield, gaining new abilities over time as they master individual weapons. 

If you wish to use this in your games, let me know! I am currently testing it in a mixed group of veterans and new players, results pending. Word of caution for using it with newer players; the Weapon Mastery system can make the game complicated for the inexperienced, but the Weapon Skills system can easily be used without also using Mastery.

What follows is an in-depth walk through my thoughts behind the design. I do not recommend reading it until you have familiarized yourself with the document, so scroll down and download that first!

Design Thoughts

The primary challenge of this design was to create something that not only provided a unique identity for each weapon, but also was simple and compact as to not require individual designs for each weapon.

For that purpose, I decided to create a system of tags that could be applied to each weapon. A tag would represent a specific weapon skill that the weapon would provide access to while wielded and proficient. 
This tag system allowed the weapon skill system to not be an overwhelming design effort, but also threatened to only add a small bit of homogenous depth to the weapons, rather than providing identities. However, the primary identity problem weapons in 5e has is the lack of distinction between two weapons using the same damage die; specifically those available to the same character. For example, a Fighter, with access to martial weapons, has no real reason to choose Battleaxe over Warhammer or Longsword, as those have the exact same mechanical effects other than mostly meaningless damage types. Same applies to the Short Sword over the Scimitar. In some cases, weapons are clearly inferior to equally attainable alternatives, making the only real reason to get them over their superiors aesthetic.

As such, rather than make every weapon distinct from every other weapon, this system just needed to add something to differentiate similar weapons. If the Fighter wants a versatile martial weapon, the choice between Battleaxe, Warhammer, and Longsword are now far more meaningful, and the same applies to Maul, Greataxe, and Greatsword, and other mechanically adjacent groupings of weapons. 

Weapon mastery started as the idea of adding additional mechanics to weapons based on the wielder's skill with the weapon. The idea was simple enough: through some abstract representation of mastery (I chose high attack rolls), a character specializes in an individual weapon, gaining unique benefits. The challenge of this design was the efficacy of higher levels of mastery pigeonholing players into using whichever weapon type they decided to start the game with. If they started with a Longsword, gained mastery, and then found a magical Greatsword, rather than be happy to find cool loot, they may be sad that they didn't find a magical Longsword. 

I decided to make the effect of mastery rather small; the player didn't have to go out of their way to get it, so it didn't need to feel like a huge reward, but I still wanted mastery effects to feel unique. The result was 2 levels of mastery for each weapon: The first providing a +1 bonus to the weapons attack and damage rolls, just like if the weapon was magical. Simple, tangible, and useful. The second, and final, level provides a unique, per-weapon effect that helps to encourage a specific use, ties into the weapons weapon skills, or lets the wielder do cool things. 

The decision to limit mastery levels to 2 keeps it simple as a design, as well as sets a clear upper limit for the character to reach, encouraging them to experiment with multiple weapons. 

In terms of game balance, both Weapon Skills and Weapon Mastery provides a noticeable bump in power for weapon wielders, especially those with access to martial weapons, which have a greater effect. To me, as a designer, this is ok for two reasons: 
1, the game's balance isn't static, and metrics by which a characters power is measured are the challenges they face and other player characters. The DM can easily adjust the strength of NPC's in combat encounters, and other player characters also have access to weapons! And if they dont,
2, The tools available to spellcasters have become more varied and effective, allowing them to naturally come out ahead of weapon users most of the time.