There are 12 types of Devotion project, corresponding to 12 Heroes in the game. You can only run Devotion projects to Heroes that you have already discovered.
The Production cost starts at 20 for the first Hero, and increases by 120 for each Hero you own.
Upon completion, it summons the Hero that project is dedicated to, and the city becomes the home city to that Hero. A city can only the home to one Hero.