A few years ago, I put some videos of loop diabolo tricks onto this site, and more recently, I put a bigger (17mb) video of a practice run of the loop diabolo act I occasionally perform on the site too. You can find them here. This section of the site explains some of the tricks in those movies, and goes into a bit more detail on some of the loop tricks I find interesting.
Diabolo on a loop string is less common than 'normal' diabolo, but it's highly versatile and opens up a huge range of tricks. You can use a loop with the diabolo inside, or as a string between both hands with the diabolo on top of the loop. Most diabolo tricks can be performed using a loop, and there are loads of tricks that only work on a loop.
Although this is a two diabolo site, but it seems a good idea to start on the basics of loop diabolo, so I've split this part of the site into the sections listed to the left, starting with one diabolo on a loop.