Q:

Is there an official repository for snaps?

"uApp Explorer is the unofficial viewer for snaps and Ubuntu Touch apps."

If you are looking for snaps on the official site for snap on ubuntu desktop, the only link you will find, links to the unofficial viewer. I am confused? Is there no official viewer?

A:

Is there an official repository for snaps?

Yes there is, but it provides only API to interact with. snap or Software Center may used to search and install them. See Click Package Index’s documentation.

Is there no official viewer?

If you mean a Web interface to browse the store, then Agree, there is no official yet.
Update: Now, there is one at https://snapcraft.io/store , Thank you Max.

