I know there are a lot of variations on this theme, so why not add a couple more! The main features of mine are:

• Two versions:
  • 10mm diameter rounded top (I'm tired of the pointy ones leaving dents in heavier things).
  • Flat top (~12mm diameter), so you can add your own rubber/silicone/vinyl bumper for an even softer non-slip support.
• Interlocking bases:
  • This is a feature on some of the name-brand versions of these items, but which has always felt awkward to use due to how those were implemented. There's just enough play in these that you can easily interlock 6 to create a fairly stable structure to provide even support under a larger area.
• Attachment holes for screws:
  • Another feature from the name-brand versions. I don't use these, but I can see them being useful for someone to attach several of these to a fixed base.
• Stackable:
  • They don't stack into a perfectly stable column, but they do stack to save space in whatever drawer/box you want to store them in.

If you'd like to generate other variations like a more or less rounded tip, the model for these is parametric and can be viewed/edited/forked at Onshape.