Even when Reforged was out, for 1-2 weeks you could have played Warcraft 3 classic again online officially on classic Battle.net! A user made this very popular post about it: OMG! I can go back to Classic TFT now. Everyone Come read! :D :)
It was easy to join, I was playing on that with some others and having a lot of fun. So many people missed out on this last opportunity though and it is closed now.