Every week I see how other players obtain items at the ends of the games. For example, parts of armor sets. I have played many hours of Counter Strike Go and in that game the loot refreshes every week. But I don't know if this system is the same in Dota 2.
In Dota 2 there is an Item drop system:
The item drop system is a feature that allows players to obtain cosmetic items for free through playing the game.
- After every matchmaking game, each player has a small chance to receive an item or set.
- All drops in Dota 2 are solely based on time played in Dota 2 via matchmaking.
- Winning, losing, or individual performance has no effect on item drop chance.
While spectating a tournament game with over 100 viewers, one or more Heroic items are randomly given out to viewers each time a memorable event occurs.
For more information about Item drop system read this.
The exact chance of getting an item at the end of the game was not disclosed by Valve but they stated:
All drops in Dota 2 are solely based on time played in Dota 2 via matchmaking.
So I guess the longer the match, the higher the chances of getting an item (something I did notice after very long games, having an increase on the number of players that usually receives items)
One thing I have noticed is that the chance is purely random and not RNG as most of the in-game chances (it does not increase if there are multiple games without receiving)