ext/         -> Implementation of TLS extensions
auth/        -> Implementation of TLS authentication methods (DHE, SRP etc.)
accelerated/ -> Implementation of cipher acceleration

Certificate support:
x509/        -> Implementation of GnuTLS X.509 certificate support (and more)
openpgp/     -> Implementation of GnuTLS openpgp support
opencdk/     -> Implementation of low level openpgp packet parsing
minitasn1    -> ASN.1 structure parsing library
pakchois/    -> PKCS #11 wrapper library

Crypto backends:
nettle/ ->   -> The nettle crypto back-end
gcrypt/ ->   -> The libgcrypt crypto back-end