This is a replica of a Holotape/Holodisk from Fallout 3/New Vegas. I based this design on the in game texture as the in game model for this item is just a rectangle. I’ve tried to keep it as accurate as possible but the only source image is the 128x128 texture which isn’t very detailed so I improvised a little with some parts.
I designed this to fit the 4mm tape found in a conventional audio cassette and to have a fully operational mechanism so it should be theoretically possible to make a fully working player for one of these with a little effort.

edit:- just added a new pic of the inside with the tape installed

Update:- it Works! sort of, just did a very quick and dirty test with parts from an old walkman and a dirll and it plays, not very well but with a proper player it would be much better. see here http://www.youtube.com/watch?v=aM91xYbEtww

Print two of both reel halves and two guides and one of each of the other parts. All parts can be printed without support. To fit together 4 M3 screws are needed (between 6MM and 10MM long). To make the item fully operational as well you would need the tape from a cassette and an extension spring or small rubber band.