Hey, it never occured or interested me until now, but is there an option where I can easily show my library to friends on gog.com or, for example, Skype?

You know, like on Steam where you can check out which games the other person owns.

No easy way, no. What I do is use Magog. You import your game list into Magog using the instructions it gives you, then you can link whoever you want the search result of a search with your game list selected.

Thank you very much :)

There is currently no official way.

As for unofficial ones, you can install Barefoot Essentials and send a chat message to Barefoot_Monkey (link ) to create you an account on [url=http://gogwiki.com/wiki/Main_Page]GOGWiki. Once you have an account, you can create a page for yourself, which looks like this:
[url=http://gogwiki.com/wiki/User:Grargar]http://gogwiki.com/wiki/User:Grargar[/url]

Gragar's way is definitely cleaner. You'll have to update the page every time you add a new game, however.

GOG developers have been working toward introducing user profiles that you'll be able to make public (it's even mentioned in the terms of use as if it were already available :D ). They haven't really said much else about it, though, and there's no ETA for this feature (maybe a month from now, maybe 6 months, maybe more than a year).

You could enter your library on Completionator and share it with the world! :D

For example, here's mine.

There's an import too, so you can bulk load your GOG games.