RNP is a set of OpenPGP (RFC4880) tools that works on Linux, *BSD and macOS as a replacement of GnuPG. It is maintained by Ribose after being forked from NetPGP, itself originally written for NetBSD.
librnp is the library used by rnp for all OpenPGP functions, useful
for developers to build against. Thanks to Alistair, it is a “real”
library, not a wrapper like GPGME of GnuPG.
NetPGP was originally written (and still maintained) by Alistair Crooks of NetBSD.