It started with an idea for a credit card sized holder for MicroSD cards so I could carry them in my wallet. In the end it became a general purpose design for a flat storage holder for any number of SD/MircoSD cards, even added possibility of a keyring hole. The holder space is divided in 4 zones like:
+---+-------+---+
 |     |    1    |     |
 | 3 +-------+ 4  |
 |     |    2    |     |
+---+-------+---+
For each zone you can specify how many SD/MicroSD slots you want to add.

The design comes with build in support that you have to remove after printing before you can use it. In the scad file there is a global variable 'Support' which you can set to false to not generate the build in support in case you have a better solution for support (like to hear about that) or use something like a powder printer that does not need the support.