At the moment I'm trying to get rid of Adobe Lightroom and Adobe Photoshop.
I looked at several programs as a replacement for Lightrooms asset management capabilities. The closest in terms of features and usability is Digikam.
One feature I couldn't see immediately is grouping of images in stacks. Luckily this is also there in Digikam. It's called - Grouping.
What I need now is a way to convert the Lightroom stacks to Digikam groups. Both programs use a SQL database, so this should be possible.