This doesn't look like "alternative to GitHub" to me; you don't need to download any client to use GitHub and having a nice web interface is one of the most defining feature of GitHub.
GitHub is a “social coding” platform that provides collaboration features (access control, issues, etc) on top of Git.
This is a social coding tool that provides collaboration features on top of Git.
It provides a desktop app because it’s peer to peer. That’s an advantage over a web UI for developers looking to avoid a dependency on a centralised third party.
You are free to continue to play in walled gardens but this is very much an alternative to that.
