at the moment Zeroshell supports:
-OpenVPN for LAN-to-LAN Virtual Private Network with TAP virtual interfaces;
-OpenVPN for Host-to-LAN VPN with Kerberos 5 authentication (included Active Directory), RADIUS (PAP, PEAP MS-Chapv2 and EAP-TTLS) and X.509 authentication;
– L2TP/IPSec host-to-LAN authenticated by using the local RADIUS.
I am not sure if Zeroshell supports PPtP VPN protocol.