Thanks for the https://releaseapp.io shout out! Reploy looks like a copy of what we are doing. Game on.
Both products operate in the same space, and are attempting to solve similar problems, but as far as I can recall Release attempts to manage all environments from dev -> production, while Reploy is specifically targeting the developer experience around managing and sharing staging environments.
The concept of dynamic staging environments is not new; I've personally built in-house solutions to solve this problem years ago, well before Release went through YC. It's not really fair to say that anyone who comes out with a similar product is "copying Release".
But, we started with the idea of Review apps for more complicated apps than heroku can do.
There are many companies trying to solve this problem in various ways, or smaller parts of it, which is good, validated the space.
I agree with the other responses; everyone is working on the same problem, but from what I've seen no one is just a copy of someone else's work.