The first, the Mathematics Digital Library (MathDL), is a digital library of mathematics questions. It was created because I felt that publishers are charging too much for mathematics textbooks. They reuse most of the material (examples, questions, explanatory text) from one edition to the next, and charge users as if most of the content were new.
Over the years I’ve taught (over 26 years!), I’ve accumulated many textbooks. In fact, I’ve a few editions of several textbooks! I thought a database of mathematical questions would be useful.
Today, textbooks have become bloated. Many pages in a textbook are devoted to examples and exercises. I’m hoping that one day, authors will not have a “exercise” section in their textbooks. They will just include links to the questions that this database provides, from their textbooks. I think this would thin down textbooks quite a bit, and make it less intimidating.