Level By Use

Instead of allocating stats/skill points or resource into improving some modifiers/stat/skill, its level or numeric modifier is determined by number of successful uses of skill/item. Using Diminishing Returns to soft-cap the modifier is advised(example only for clarity):
http://videogamedesign.wikidot.com/mechanic:diminishing-returns

Example:
A skill power is determined by number of successful uses:
using a formula like 1+log^1.05(Number_of_Successful_uses) determines the factor equivalent to level multiplier of skill.
for 10000 successful uses of skills=1+log(10000)=1+9.210340372=10.210340372 skill level.
i.e. no skill points are gained, smooth power progression as the skill is used.
if for example skill damage is 10 per skill level the damage will be 102.10340372

Example2:
An item modifier stat is changed by number of successful uses(permanently and only linked to the item, not character using it):
+1 damage per each 100 successful hit with this item(up to 10000 max bonus)
for 10000 hits connecting, it would add +100 damage to item modifier.

Variations:
Idle use(item equipped, skill selected) gains a small bonus per minute.