The following tags are actively used at the moment:
Most of them should be self-explanatory, and for the others, here are the explanations:
bounty
There is a bounty put on these issues! Typically, these are handled via FOSS Factory.
fixed_in_debian
This tag is used to tag items that have been fixed in the Debian GNU/Hurd distribution, but not yet in the upstream sources.
open_issue_documentation
Used for tagging pages / items that need to be handled / improved for documentation purposes.
open_issue_porting
A list of open issues in porting software to run on GNU/Hurd systems. This list also includes toolchain-level items, items that are either already solved in Debian GNU/Hurd systems (tagged fixed_in_debian) or being worked around, so if you're out for working on application-level porting issues, then perusing through the list of Debian packages that need porting may be better.
stable_URL
These pages are tagged as having a stable URL. That is, they're linked to from external pages, and their locations should not be changed needlessly.