Installation exits basically define the script based on your action before you login into the system or after you have logged out of the system.
SAML2 IE came before multiSSO but both are used for IDP and external authentication mechanism.
If you have multiple IDP configured, then the system will use multiSSO and prior to it SAML2 were used for single IDP.
http://wiki.servicenow.com/index.php?title=Installation_Exits#gsc.tab=0
Please mark correct/helpful based on the impact of the response.
Thanks
Gaurav
