Yags has been used in the following campaigns.
The Isle of Taneith
Taneith - was the first campaign to use Yags. It was a celtic setting, and was the first campaign in the world of Eorthe. Some of the plots hinted at in that game have survived to later campaigns.
The campaign introduced the Giants, and their preparations for a coming darkness.
Cadwold - in the year 1230, this was the first of the
Habisfern - campaigns. The focus of the campaign was around the war of independence in Cadwold, and the rise of the power of the Druids of Danuch.
It was going to introduce some of the plot from the Taneith campaign, but ended (I forget why) before that really got off the ground.
A short campaign set in the Babylon 5 universe. This was the first introduction of modern firearms and psionics. It was set a few years before the start of the television series, and involved a Human/Narn crew of independant merchants. It didn't last very long due to availability of players.
Call of Cthulhu
A one shot adventure where I used a quick and simple version of Yags for a Cthulhu adventure. It was relatively rules light (in the sense of making up the rules as I went along), but introduced the idea of an attribute range of 2-5.
This campaign started with a new group of players (well, new to the world of Eorthe at any rate), and was written to tie in the loose ends from the previous two Eorthe campaigns - both Taneith and Cadwold. It was set in 1229, just before the start of the previous campaign. By this point Yags was starting to stabalise (version 0.5).
Towards the end it was running concurrently with the Harn campaign which started later, but due to being stuck on a project in London, I ran out of time and energy for running anything on a weekly basis, and the campaign ground to a halt.
I decided to run a monthly campaign set in Harnworld, and produced a new magic system (based around the HarnMaster one) for this. It ran for a while, with the plot being based around a cult of Morgath that was planning a very big ritual involving the souls of dead Shek-Pvar and the help of the orcs.
Eventually there was possibly going to be a crossover into Middle-Earth (I had a plan to run an exploration of Kiraz, where gateways to Moria would be found), but again London sucked all life out of me, and I no longer had the energy to run it.