GOG.com announces that Fallout, Fallout 2, and Fallout Tactics are no longer for sale on their DRM-free marketplace, apologetically, but vaguely citing "circumstances beyond [their] control." Here's the explanation of how this impacts people who have already purchased one or more of the seminal RPGs:

All those who acquired Fallout, Fallout 2, or Fallout Tactics on GOG.com prior to the date of removal (that is before Tuesday, December 31st 2013, at 3:59PM GMT), will still be able to download the games' install files (as well as the bonus content) via the "My Games" section of their user accounts. Gift-codes for these three games acquired in our recent giveaway are no longer valid. However, if you own a gift-code for any or all of them that was purchased outside of the said giveaway, you'll still be able to redeem it in the foreseeable future.