I came about ATRA Wiki and wanted to get an account to be able to participate. The site seems clean and maintained, which is good for a Wiki.
However, this may be exactly because people cannot participate. The 'log in / register' link used to give an invalid email id to contact (for an account). Now it just leads here.
Does anyone know the story behind this? I think they should rather close a wiki if people are not able to also edit it.