Box Organizer for Unfathomable board game. It fits sleeved cards very comfortably with lot of space left for future card content (miniatures are an unknown quantity at this point)
There is also a "plug-and-play" card holder for skill cards with a piece indicating their type.
Material update: due to war in Ukraine we had to switch from plywood to MDF. It is locally available material, looks slightly less shiny than the plywood on the pictures. On the flip side, this material is significantly cheaper, led to reduced price.