So this is a really niche design. These are plastic dividers for the "Dominionizer" handmade organizer for the cardgame Dominion. This organizer is very well made by the fine folks at DominionCaddy on Etsy. Here is their link:

https://www.etsy.com/shop/DominionCaddy?ref=profile_header

The organizer comes with wooden inserts to separate the various editions & expansions for Dominion. They include excellent laminated card dividers which separate each type of card within each expansion. However, it can get a little dizzying to try to find the correct expansion you are looking for so I replaced the wooden dividers with these taller plastic ones. They are embossed with the name and icon of each expansion. The design is modular so that you can have your cards fixed (untabbed) or floating (untabbed). A bit of good advice - only use floating for for the first expansion in each column.