Here's something I haven't stumbled on before - the Game Innovation Database.
It's been around a while, so you may be familiar. In fact, it originally began in 2004, going through various incarnations and student teams, and for the last year has been a somewhat confusing, but rather intriguing Flash map.
It's a family tree for innovations. The site states:
"The goal of the Game Innovation Database is to classify and record every innovation in the history of computer and video games, while displaying their relationship to one another. It is our belief that all innovations can be traced from a previous entry, much like a family tree. As such, each innovation has a parent, and the potential to inspire future growth, or children."
So you pick an innovation, starting with the 1954 naughts and crosses game, OXO, and spin off from there. Or you can throw in a name into the search engine. It's not about developer links, or game series, but the games that demonstrated an advancing innovation first, and those that led to this, and were born of it. Alongside the map, oodles of information appears in a text box on the left, with history, details, and screenshots. It's a fascinating browse.
(Another interesting thing about it: Browse the site for a while, and then switch back to a regular, white-background website or Word doc, or similar. Man, that hurts.)