MetaFilter Projects is the section of MetaFilter where 'self-linking' is allowed. It is a place for members to announce their projects and receive votes and feedback from other members. If someone else on the site thinks your project is worthy of posting to the front page of MetaFilter, they can easily do so via a button on the feedback page. A fun success story is this teaching assistant's project that was then posted here.
Prior to the introduction of the Projects section of MetaFilter there used to be a mailing list called MetaFilter Projects (archives) that members (and anyone else) used to advertise their projects, websites and other such things. It operated from 2001 through 2004.