AD&D was Gygax's new ways of playing OD&D.
AD&D 2e was Zeb Cook's way of playing OD&D.
3e was Monte Cook, Jonathan Tweet, and Skip Williams's way of playing OD&D.
4e was Rob Heinsoo's.
5e was Mike Mearls's.
Pendragon was Greg Stafford's Authurian inspired OD&D.
Traveler was Marc W. Miller's OD&D in space.
OD&D defined itself, not as a set of rules, but as an framework for creating one's own personalized game. Without OD&D none of those games would exist. They all derive themselves from it. Some of those personalized homebrews also have a price tag, but they're all equally valid ways to play the game.
- "Will enjoy playing DUNGEONS & DRAGONS®. Its possibilities go far beyond any previous offerings anywhere!"
- "As with any other set of miniatures rules they are guidelines to follow in designing your own fantastic-medieval campaign. They provide the framework around which you will build a game of simplicity or tremendous complexity — your time and imagination are about the only limiting factors, and the fact that you have purchased these rules tends to indicate that there is no lack of imagination — the fascination of the game will tend to make participants find more and more time "
- "Actually, the scope need not be restricted to the medieval; it can stretch from the prehistoric to the imagined future, but such expansion is recommended at such time as the possibilities in the medieval aspect have been thoroughly explored. "