I think it's kind of funny they start out by saying:
At first, we have never copied any materials from GitHub so this is not problem.
But later when you scroll to their footer it says:
GitBucket is a GitHub clone powered by Scala.
At first, we have never copied any materials from GitHub so this is not problem.
But later when you scroll to their footer it says:
GitBucket is a GitHub clone powered by Scala.
There's nothing wrong with building a compatible clone of a proprietary program or platform; that's a valuable contribution.