This is not a "full clone" but "something like GitHub" but for your own private server.
> I understand that the server-side implementation is based on GitHub as a black box
No, it's not. The serverside is implemented in Scala using a JGit as a GIT library for the files and H2 database for saving the metadata.
I was just wondering about theoretical consequences of cloning UI/tool of a successful company software with the reason of the tool/interface being too expensive.
If it's done for learning the technologies then it's "for educational purposes" and probably falls into another copyright use category that is more permissive.
The UI was not cloned either :). The UI is a Scalatra template (Twirl) and a Twitter Bootstrap style. It could be customized in any possible way and look the user would wish, but so far the developers are concentrating on the basic features.
From a quick scan of the sources, H2 seems to be an hard-coded dependency. Do you have any plan on abstracting the Slick driver to allow others DB providers ?
I'm not the developer of the project, but database independence was not requested so far :). I suppose if users will ask it, it will be added. H2 suits however very well all the needs, it has a web based Admin UI that can be simply reused, and it's performance is fantastic: http://h2database.com/html/performance.html