Here are three different designs to hold DIN A7 (74mm x 105mm) index cards. The top is chamfered, the cleanest look has the "box" version.

You can fully customize each holder using OpenSCAD and the included .scad file:

• Choose from 3 designs, "box" (cleanest look), "leg" (fastest print), "double_leg" (super stable)
• Change the card size, so you can hold playing cards, several index cards, etc.
• Change the angle to easily see the cards.

Have fun!