From the introduction:
What's the Collective and "Everything in Print"?
I use literally Everything in Print, which means if it has appeared in any AD&D or D&D product anywhere, you can use it. For example, you can be a 2nd edition Athasian Half-Dwarf race using the 1st edition Dragonlance Knight of the Rose class. Both Rangers exist, and are seperate classes (Ranger1 and Ranger2, the number indicating edition). Both Bards similarly exist, plus the "Not So Hard" Bard from Dragon Magazine, and the Athasian Bard as well.
Unfortunately, not everyone owns everything in print, and carrying around 40+ hardbounds from 1st throught 3rd edition (and then having everyone at the gaming table share) is cumbersome. Thus the Collective came into being, which is (basically) the charts of the various supplements put together into one product. The Collective does not explicitly describe how to use these charts, as familiarity with basic AD&D material is assumed. The Collective also makes many changes to those charts.
User summary:
The D&D Collective is provided in several HTML versions with varying levels of detail.