Thanks for noticing this. Seems as if GOG changed the title to "The Legend of Heroes: Trails from Zero" so I will change it as well. The title under which you should find the games in the list is always the title that GOG uses. If something is not correctly listed, feel free to tell me here or via chat :)
Well, as achievement fan your wish is understandable, but keep in mind that there are people out there who find achievements distracting and in opposite to client based achievements you won't be able to turn off ingame achievements. Does not make a difference if the game does not show a popup but some actually do. So as usually the medal has two sides.
Thanks, will add this to the list immediately.

I don't agree. There's nothing distracting about how it's done in Trails from Zero. And there's nothing stopping a developer from having an option in game for displaying achievements or not the same as an option to enable rumble or not. There's no need for an online service for this unless it's to show off to others.

If you were referring to the exact same way it is handled by Trails this this is true. I thought that you were talking about ingame achievements in general and even though of course it would be possible for each dev to make ingame popups optional that's rarely the case (tbh I don't know a a single game that does this). Also, the bragging factor is probably something most achievement hunters would not be willing to drop if we are honest and showing the achievements to others is much harder without a client. However, there's no need to discuss this even further since it is all theoretical - devs won't quit using the easy way which is achievement implementation through a client - so let's just be happy about every dev who is willing to go the extra mile here :)

Just added MouseCraft to the list.

Return to Monkey Island has in-game achievements.

Nice. One more reason to get it. Thank you.

Prodeus has in-game achievements.

This isn't actually true; many GOG games will unlock Galaxy achievements even if you don't have Galaxy running. The games use Galaxy library plugins included with the game, which track achievements. I rarely use Galaxy (mostly just as a downloader for larger games), I have it set to not automatically launch, and I never run games through Galaxy. Yet if I do run it, I see a bunch of games that have unlocked achievements along with the dates they were achieved. Not all though...not sure why some games (that definitely do have Galaxy achievements) register and some don't. Time tracking, though, does seem to require Galaxy to be running, as even the games with unlocked achievements have zero playtime recorded.

One example of a game with different in-game achievements vs. Galaxy achievements is Dysmantle. (And it's a game which does not register Galaxy achievements...actually, looking through my list briefly, there does seem to be some correlation where games with in-game achievements tend not to register Galaxy achievements without Galaxy.)

In addition to being somewhat different, the in-game achievements (called "medals") have progressive bronze, silver, and gold levels, whereas regular achievements are binary: you either get them or you don't. Plus unlocking medal levels gives you XP in the game and regular achievements don't really do anything aside from existing.

Thanks for the additional info, much appreciated. I'm currently playing my first game with achievements, Pathfinder Kingmaker. This is one where the achievements are in Galaxy, and it's fun to see them pop up. One thing I'm curious about is the overlay. I thought I would be able to see achievement activity in it but all it seems to show when I open it is an option for chatting. The box on the right side of the screen, if it's supposed to contain something else, just seems to have an endlessly spinning cursor.

You'd want to start a new topic for that; this one is really just supposed to be for in-game achievements only, so I don't think many here know much about Galaxy-related things like overlays (I definitely don't).

Fabled Lands also includes in-game achievements

I can confirm that Blasphemous does have in-game achievements.

The overlay lost its achievement list with the introduction of Galaxy 2.0. As far as I know, no explanation has ever been given.

Thanks!

Thanks, will add it.

1) It depends on the way the devs have implemented achievements. Some achievements will be unlocked retroactively as well so it it does not matter if you unlocked the achievement while being in Galaxy or not ... but the achievement will only unlock WHEN you run in Galaxy at least once. So in the end you still do need the client to use achievements. It does not matter if you have to use the client multiple times or just once. Without the client running (at least once) achievements won't work in the case of non ingame-achievements.
2) I am also pretty sure that you will at least have to run the Galaxy service so without Galaxy being installed no achievements.

In case of ingame achievevements though it does not even matter if you have Galaxy installed or not.

No, you won't see the list of the unlocked achievements in the overlay (which basically is just a chat window as you figured out by yourself) as it is the case with Steam games. However if you enter the installed game site in Galaxy and click "progress" you will see which achievements are unlocked, which achievements you are missing and how many are secret. Sometimes devs implement those wrong though and you won't see that list (all achievements hidden in dev mode) but normally that will be the case. If you should need further instructions feel free to send me a chat :)

Can't even remember that Galaxy 1 had an achievement list implemented in the overlay ... then again .. it's been a long time.... and I am old :D
Thank you both. On the list it goes.

Quake Enhanced has ingame achievements. Thanks to Hikage_XjS for letting me know :)