I picked up my fourth PowerBook 100 yesterday - a working unit (I haven't confirmed this yet) with an external floppy drive. No power supply but I have a few of these now. Hopefully it will have a working hard drive and more than 4MB of RAM (I can hope).
With enough time I intend to build as many working examples as I can. The other three have power-up issues (although at various times ALL have worked).
For those wondering, "Derringer" was one of the alleged code names for the PowerBook 100 in production (see this photo). Derringer/Deringer is also the last name of a gentleman who made small firearms. Given that the PowerBook 100 was Apple's second attempt and first real success at a laptop/notebook computer (the Portable being barely that), I can see the link.
Edit: Sadly, it doesn't boot (why am I not surprised?). It does have an Apple 20MB 2.5" Connor SCSI drive that may work though. As far as RAM goes it looks like 4MB (again, still searching for the elusive 6MB upgrade card).