Brink of Battle is now available as a .pdf over on Wargame Vault. Check it out.
From the announcement:
Wargames Vault is now carrying the PDF version of Brink of Battle: Skirmish Gaming through the Ages. You can find it here.
Use the models you have to play any time period from history in gritty man-to-man skirmishes! Also check the Brink of Battle website to download play test matierals for the Fantasy and Sci-Fi supplements!