Yes I know, GOG users have received yet another game without a basic feature available in the Steam version, so I am humbly asking developers to add achievements to GOG Galaxy.

Astalon is great, and I would love to have this bonus feature in the game.

I second that. Most of the times developers send meager versions to the GOG... This is really unfortunate...

I was about to buy it, but checking forums first, I see your message and decided not to do it.

Hope they reconsider and add the other features to the game.

third this!

This game has invisible achievements in development mode and it can be patched to make them work. Please refer to the broken achievements thread, section BROKEN ACHIEVEMENT FIXES in the OP for further information about this.

The direct link to grab the patch is here. It includes a readme that tells you how to install it, but having rudimentary command line knowledge is recommended in order to apply the patch.

Also important to note is that the game has two test achievements defined, so it's not possible to unlock 100% by playing the game at the moment.