Here is the sort of game I'm looking for:
* Can be played to completion in 5 minutes or less (casually with no unintended major skips). If this is only possible on some modes, such a mode must be unlocked from the beginning.
* No save feature (I would prefer the game to be self-contained in this sense, and not have to worry about things carrying over between playing sessions).
* Most genres are OK (no FPS or fighting games), but the primary mode of play should be single player.
* High replay value (the reason should be obvious; I can tolerate low replay value if the game is long enough, but a 5-minute game needs to be one that I can replay immediately after finishing).
* Must not contain content that I would consider offensive.

So, does GOG have any games of this sort?

(The closest I've encountered is Crimzon Clover's time trial mode, but even that game saves the total number of stars earned, which is used to unlock what is apparently the best ship.)

Edit: Why the low rating?

First game that came to mind: https://www.gog.com/game/race_the_sun

Racing games of any kind should fit your criteria in general.

Maybe "Book of Demons"?

As mentioned on the gamecard: "Book of Demons respects your time. It features the Flexiscope engine which allows you to divide the game into sessions of any size. It even learns your pace of gaming and predicts the time to complete the next session."

Book of Demons is a bit longer than what she asks for. Game sessions can be scaled between something like 10-15 min and more than an hour, not under 5 mins.

Well then thats not of choice; thanks for clarifying.

nevermind

Downwell, maybe.

The 5 minute bit makes this thread seem like more of a social experiment than something that merits real recommendations though.

and his other threads had similar 'social experiment' vibre

She has answer me whom exactly in pm.

Are you looking for just GOG games or they can be also free games?

One of the best "shortest games" I like is Strange Adventures in Infinite Space which is now free. It's the first part of the series (I also played and liked Weird Worlds: Return to Infinite Space) but the rest is not free and not on GOG.

I think you can lose a pinball game in less than 5 minutes. Does that count? Too bad these tend to save your hi score.

"Super Hexagon". A regular game lasts seconds.

Spaceplan : http://jhollands.co.uk/spaceplan/
Well, technically it takes more than 5 minutes to complete, much more, but the active game time should be under 5 minutes. As a fan of cookie clicker you might get a kick out of this.

I play a fun game sometimes where I decide I want to play a game, load up my gog library,
look around for 5 minutes for something to play, realize I can't decide what to play, and then quit.

I never seem to win but I'm not sure if I lost either...