Minigames or activities which are limited by time. Like runescapes "dailys".

Daily tasks

Exp Dungeons

Dungeoneering dungeon where npcs drop coin loots (that you can take out) and skills give massive exp, but is one-time only before depletion and you can only move into the next room one day at a time. Resets at the end of the week/month.

Point system based on active play-time

Daily chests

Fixed rewards each week for logging in each day
Store purchase for better rewards