Common Errors in English is a website that has been up and running since March 1997, as its maker, Paul Brians, told me. Does that make it the oldest language advice website that has been about? Quite possibly It has also been up for twenty years this year, and has just been given beautiful a new interface.
It was given this new interface (an 18-month job no less!) not because Paul asked for it, or as a twentieth birthday present, but because it was recognised that it was “by far the most popular academic area on the entire university Web system”, as Paul emailed. Washington State University, well done to give recognition to the importance of language advice on the web!