using blockchain.info api, it would take really a month to get an API key 
my two applications got rejected recently
I don't understand why they are so restrictive about their API, but if you really need one to work with, use block.io, i like them because it is really easy to use, easy to generate and manage accounts, and they support bitcoin litecoin dogecoin.my two applications got rejected recently
I didn't tested the others but i plan to do it soon.
Talking about these APIs is there a website who tracks them ?
You do not understand ?
Because it costs them lots of money and ressources to maintain the API up, and to answer all the technical issues for the API users.
Why not just make an API like that one, for free and you will have an idea of its complexity.
Block.io sucks.
I know how complex it is, and i know how much ressources it consumes, but why other API providers do it without restriction ?
Block.io is a simple API who does the job, now for security considerations i didn't went too much in testing as i never had to use it in a production environment, i just know that it is accessible, easy to use, clear UI. And these are very appreciated qualities.