IPSec, GRE, DMVPN

GRE doesn't provide security, but it does provide a standardized way of bridging the gap between two routers, making it look like there's a dedicated local link between the routers.
GRE has multiprotocol support, including protocol 47.
GRE supports broadcast and multicast traffic, whereas IPSec only supports unicast traffic.
Routing information has to be multicast or broadcast based, and as GRE supports that, it allows routing information to be sent.
GRE can be set up as a collection of point-to-point GRE links or multipoint GRE.
GRE doesn't provide authentication services.

DES and 3DES are methods of providing IPSec confidentiality.
The Diffie-Hellman, or DH algorithms are a method of providing IPSec confidentiality through symmetric keys.
RSA is an asymmetric encryption algorithm used to provide IPSec confidentiality.
AES is a symmetric-key algorithm used to provide IPSec confidentiality.
HMAC-SHA-1 and HMAC-SHA-2 are used to provide IPSec integrity.
HMAC-MD5 is used to provide IPSec integrity.
Preshared keys and RSA signatures are used to provide IPSec authentication.