This is a spherical keycap with a Cherry MX stem. The design is meant to be similar to the SA keycap profile. This design has been around for a while since I made it available on Geekhack, and it has had a few hundred downloads there since I posted it. I'm sure the Thingiverse crowd will find plenty of ways to customize it.
This seems to be the only spherical profile cap I can find on this site. Most everything here has a DCS or OEM Cherry profile. This is designed to be slightly taller than a DSA cap, and slightly shorter than an SA cap. A figure of this comparison is included on this page. This means that there is plenty of room to add "stuff" to the face of the cap (letters, numbers, tiny robot faces, etc.) without negatively impacting the overall profile of your board.
The face of the cap is supported by some filleted bridges which will clear the casing of your MX switch upon keypress. This also improves the structural characteristics of the keycap for those of us that have fingers like tiny hammers.
Text can easily be added to the face of the cap. I have included an example I made with a quote from American Psycho in the files.
Keycap stems are tricky to print, as they tend to demand tight tolerance. This was designed with a little extra tolerance for thermoplastic expansion. If you decide to use it often, print a quick one out first to see if the cruciform fits snugly onto your switches. The versions depicted were created on a laser sintering printer, rather than an FDM printer.
Enjoy! Please report back any makes or mods of this design so I can see my stuff in action.