Holy! I didn't expect to see this mentioned on here..haha
Ok, these are kind of a pet hobby of mine, so don't mine if I go on a bit..

The original was the Gyro-ring with big plastic beads (with metal on the inside edge of each) on a metal ring, made by Fascinations:
http://www.fascinations.com/Gyro.htmLegend has it that at some point in New Zealand, a person's house burnt down with a ring in it, melting away all the plastic, leaving only smaller metal beads on it. People found that ring and started to use it. They found it was better and faster and eventually someone started to build their own.
Eventually that would be refined and be made officially as the Jitter Ring by Island Edge Inc. in Hawaii. Those got more and more popular and I think attracted the attention of High Performance Kites in Hawaii which had both a kite team and yo-yo team and created a ring one called Team Jitter Ring, recruiting players mostly from New Zealand.
Eventually that would also get wrapped into Bandai's big skill toy push in Japan in the late '90s. They produced their own Jitter Ring with Island Edge (mostly the same except for Bandai printed on the sides of the beads) and held contests, etc.
In Japan, the level of play went crazy and all kinds of amazing tricks were created, including lots with two rings at the same time. Unfortunately in the years since, the interest really died out while yo-yos was able to keep going. I think Island Edge finally went under, as well as the various knock-offs (like the Chatter Ring).
However, some time during all of that, Fascinations made their own metal-beaded ring called the Gyro-ring Pro, which they are still manufacturing. While I've heard it isn't quite as good as the Jitter Ring was, it can work well once broken in.
Takubo had the best instructional site (also in english!) and while it seems partly down, the tricks are still up:
http://idobata.dokidoki.ne.jp/takubo/jitter/e-jitter/tricks/This might also have some of the rest backed up, though I can't connect to it at the moment:
http://www.idobata-company.com/jaringa/This old site also has some info:
http://www5.wind.ne.jp/takachi/jenglish/Last but certainly not least, check out the videos I had captured a while back:
http://yoyoing.com/shawn/videofiles/jitter/Quality isn't the greatest, but I'm working on re-capturing the freestyle footage and hopefully making a new site to promote the rings. I'm really afraid that it is going to totally die out, but maybe it can be revived somehow..
For anyone that's going to use one, try to keep it clean. You can wash it with warm soapy water and run some cloth or a paper towel through the beads to clean the inside edge. Some people wear thin stretchy gloves to both cushion the hand and keep your hands from getting black (which I think has to do with sweat reacting to the steel or something). Though the black stuff washes right off, so no big deal anyway.
As time goes on, the ring will become "faster" and you can slow it down again by scraping the large ring evenly on a surface like concrete. The breaking in period will eventually even out the beads so that they stay togeter as a bunch instead of separating out. Just move a "slow" bead (rises up above the rest on a normal jitter) to the bottom and clean the ring when it gets weird, and it'll even out over time. Can also do lots of supersonics and tomahawks and stuff to break in faster.
I'd love love love if some of you take a liking to the rings! It is one of those things that isn't as impressive to look at but is really fun to use and has dancing possibilities. I even have footage of a person putting one on fire.

Also one of the few skills that works well for someone who is blind since the sound and vibrations through the ring give a lot of non-visual feedback.
Shawn