Remember in The Mote in God's Eye when the Motie miniatures start breeding in secret on the MacArthur, altering the ship for their own needs?
I first read that book when I was about twelve, and (as usual) one small detail really lodged in my brain. The little watchmakers, bred to fix and improve things, weren't entirely undetected, but the Mac's crew didn't say anything about them because they were so useful. In particular, one security officer woke up to find that a miniature had measured his hand and used a secreted polymer to reshape the handle of his sidearm for ergonomic perfection.
Again, lodged in my brain. I dunno exactly why, but the image of getting the same effect by putting some goop on a handle and squeezing it into the shape of my grip just stuck with me for years.
Which brings me to my point:
A silicone compound that molds like clay and cures overnight at room temperature. The inventor notes its usefulness for repair, for protecting wear-prone surfaces, and for adding non-skid grip to parts and tools, but she doesn't sell it for any particular application; it's for _all_ applications. The first run sold out in sixteen hours.
The obvious comments about hacking, ah, intimate tools have been made, and I can't say I didn't go there too. But man, does this ever have my inner geekling wanting to save up for a Glock and make my own Motie-blaster.