Where to find it:
Petrov Defence - Games in PGN - 10,000 Games.
Base

Database
The Grob Attack in CBV. 8000 games?

Herbie Eröffnungstheorie: Die Owen-Verteidigung 1.e4 b6
Eröffnungstheorie: Die Owen-Verteidigung 1.e4 b6
Downloads at bottom of page.

e4e6.com - Home
The page is in Italian. But where are the games?

Antiques, Perle Antiche, Dossier
Downloads in many formats.

Chess Tournament and Match History
A history page of great players with games added.

Chess Games Links maintained by Lars Balzer - Links to chessgames around the internet which you can download for free

Annotated chess games collections of famous players
Games in Fritz, CBV.

Many Openings:
[Chess File Downloads -- PGN: Openings] >> Chessopolis! <<

Chess Openings Database | Free PGN Chess Games | ECO C03 French, Tarrasch
2.6 million games.

The Center Game:
Chess openings: Center Game (C21)
Note - Free total downloads for members.
Chess Games contains Openings by ECO number, and played by GMS.
C21 is one sample.

Free Software Windows and Mac for Opening study.
Includes Fritz, and SigmaChess (Mac program).
Chess Openings Links

Encyclopedia of Chess Openings
ECO for downloads.

I want free book on openings DeFirmian_Nick_-_Modern_Chess_Openings_MCO-15 plz help

Umm... no. That book is pretty recent, so you aren't going to find a free copy anywhere. Go buy it if you want it that badly. Authors and publishers won't keep writing and publishing books if they aren't getting paid to do so. And it's a violation of copyright to distribute those works for free.

--Fromper

I know of a couple places where it’s possible to download literally hundreds of bootleg copies of chess books, including MCO-14. When I wanted a copy I realized that it would be rather difficult if every time I wanted to check out something to have to do it off the computer screen. Also printing out several hundred pages on the computer would ultimately cost about as much as the book. Reluctantly, I decided to part with the cash. There’s the legal thing too.

There are some nice links there, thanks!

I agree, better to buy the book than wait a year or two until it becomes available for free. The book isn't that expensive, really.