I usually check the NP-compendium from Pierluigi Crescenzi, and Viggo Kann when I want to know the APX status and approximability results of a problem.
However, I understand that maintaining it is a lot of work, which explains why it is not up to date in some cases. By not up to date, I do not mean non-exhaustive, but that better results on some problems are not included.
Does anyone know an equivalent and more specific website focused only on approximation, which would be more up to date ?
I am not really asking the same question as this one, or this one, but I understand that they may bring the same answer.
Remark: The last example I found was on the Minimum Steiner Tree with distance 1 and 2 on complete graphs, which is said to be approximable in 1.28, but there is a paper from 2009 which provides a 1.25 ratio. It may have been updated.