After 16 years GTAT.org shut down on 20th May 2018. Same for gtat.org at facebook, @dracogtat at twitter and on youtube.
See reasons and details at the shutdown gtat.org blog post at dracoblue.net.
Update end of 2020: There is a community based new version (started in 2020) by ex-admin members at gtat.pro.
- Draco