This is incoming.debian.org, a service which provides access to uploads immediately after they are accepted into the archive. It is primarily for the use of the Debian buildd-network but is publically available.

Most Debian suites have an equivalent buildd-SUITE available under the debian-buildd directory. These can be used in the normal way via apt's sources.list. For example:
deb http://incoming.debian.org/debian-buildd buildd-unstable main contrib non-free

 Name                    Last modified      Size  Description
 HEADER.html             2014-08-16 21:35  598   
 README.html             2016-10-12 04:58   50   
 debian-buildd/          2016-05-18 10:41    -   
 robots.txt              2014-08-16 20:50   26   

Last updated: Wed Oct 12 04:58:59 UTC 2016