I learned the Achillles defense, the Medcalf defense and much more (thanks Alan and everyone else who contributed!) from the TwixT pages on wikifoundry.
But, in stopping in tonight to check on something, I discovered it has been shut down.
The WetPaint Twixt Wiki was created many years ago by Kd Hoffmann. He wrote several articles, and there were more contributions by David Bush and Alan Hensel. I hope I am not forgetting anybody. I think that WE ALL wish that those pages could have been archived for future players. I, personally, did not have the needed computer expertise to accomplish this, and nobody else ever did this task, either. Thus, those lessons are now gone.
If you check on the Wayback website, it IS possible to access SOME of the old materials - something of a pain to do this, and most of the materials lack diagrams, so are near useless. Here, for example, is the starting page: