I don't agree with comparisons like that. I had two developers one making $10k more that the other, both about the same quality I would say. I didn't set their salaries, they had salaries negotiated when they joined the company. I thought it was unfair. It's not. Everybody has different skills, work ethics, productivity and on top of that expectations. The guy with $70k always complained about salary while $60k guy was completely happy.
It's up to everybody to negotiate salary that makes them happy, if you are not able to move on somewhere else where somebody will pay you what you are asking for.
However, putting all this aside, this application could be useful in environments where you have at least 5-10 people with the same skills, seniority, productivity, otherwise you are comparing apples and oranges.
Also, a lot of companies prohibit you from discussing your salary with other co-workers or not?
It's up to everybody to negotiate salary that makes them happy, if you are not able to move on somewhere else where somebody will pay you what you are asking for.
However, putting all this aside, this application could be useful in environments where you have at least 5-10 people with the same skills, seniority, productivity, otherwise you are comparing apples and oranges.
Also, a lot of companies prohibit you from discussing your salary with other co-workers or not?