When you first sign up for GOG there's a half dozen games you get for free to start you off. So how often do they update that? I've seen people with gift codes for things like Teenagent so they had to have been selling them at one point.

The free games you get at signing up are pretty static overall, but we periodically get free games for various promotions, and quite regularly at that. The last one was not so long ago, where Dungeon Keeper 1 was free, and DK2 had a big discount. Before that was the Fallouts...

And you can easily make a gift code for free games, but they sometimes limit their usage to the extent of the promo, for fear of people selling them later on.

long ago it was possible to create gift codes for free games. (not sure if still possible)

To my knowledge the games that are free at all times have always been that way, They are added to your account automatically now but when i joined they werent lol.

Other games are occasionally free for a limited time such as Fallout before the rights changed and the games pulled from GOG, for those you have to actually add them as though they were a purchase.

It is, it just has no purpose unless the recipient doesn't have the game yet. It's an easy way to give someone a head's up about a promo they could otherwise miss.

Ah well, thats 2 things ive learned today, Im off work tomorrow so the booze should counter-balance this increase in knowledge

As far as I know, pretty much all of these games have always been free on GOG. It's just that you can technically "purchase" them like any other game, because "new" free games are not automatically added to your account.
For example, last year Flight of the Amazon Queen and Stargunner were added to the catalogue, but if you already had an account before that, you had to add them to your library manually, complete with checkout and confirmation e-mail. Something similar used to apply to the temporary giveaways, where they just set the game's price to $0.00 for two days, but they ditched that with the recent Dungeon Keeper giveaway. That's why someone can buy a Teenagent gift code for a laugh.

Keep in mind that several of the permanently free games here are regular "freeware" anyway, such as Beneath a Steel Sky or Tyrian 2000.

But it DOES have a purpose. Trolling. "Hey guys, here's five hundred gift codes!"

I know I used it before they removed the possibility (then it was added back again after a couple years).