On Stack Exchange sub-sites it seems to be a common practice to refer to other Stack Exchange sites by abbreviating the ".stackexchange.com" part of the domain to simply ".se" (often capitalized), as in "math.SE" or "unix.SE". These aren't actual Stack Exchange domains, but they could be, answering only to GET on the root path and redirecting to the relevant .stackexchange.com URL.
Pros:
- Leverages an existing community custom from an abbreviation convention to actual references to the relevant sites.
- Shortens getting to the main page of a site by 15 characters.
Cons:
- Some domains such as unix.se are already in use, which at the very least complicates things.
- Introduces an inconsistency if .se domains for some important sites cannot be bought.