These are all implementations of Single Sign-On (SSO):

Product Name	Project/Vendor	Type	Description
AccessMatrix USO[1]	i-Sprint Innovations	Commercial
OpenOTP & TiQR Server[2]	RCDevs	Commercial and Free	OpenID and SAML with OTP (OATH Tokens, Yubikey, SMS, Email) and QRCode Login
Active Directory Federation Services	Microsoft	Commercial	Claims-based system and application federation
adAS SSO[3]	PRiSE.es	Free Software	Advanced Authentication Server (SSO)
Athens access and identity management	Eduserv UK	Commercial
CA SiteMinder[4]	CA Technologies	Commercial
Central Authentication Service	Yale University	Protocol
ComponentSpace SAML[5]	ComponentSpace	Commercial	SAML SSO for ASP.NET
CoSign single sign on	University of Michigan	Academic	SSO for Michigan University
Distributed Access Control System (DACS)	Distributed Systems Software	Free Software
Enterprise Sign On Engine	Queensland University of Technology	Free Software
EmpowerID Federation Services[6]	The Dot Net Factory	Commercial	Identity management cloud and corporate single sign-on
Evidian Enterprise SSO[7]	Evidian	Commercial	Enterprise single sign-on and authentication
Evidian Web Access Manager[8]	Evidian	Commercial	Seamless internet-to-intranet SSO access (SAML support)
Facebook connect	Facebook	Facebook specific SSO	Facebook SSO to third parties enabled by Facebook
Forefront Identity Manager	Microsoft	Commercial	State-based identity life-cycle management
FreeIPA	Red Hat	Free Software
Geneous SSO-Module[9]	Proatria	Commercial	Geneous software SSO-Module
Gigya SSO[10]	Gigya	Commercial	Social IdM SSO
Hitachi ID Systems	Hitachi	Commercial
HP IceWall SSO[11]	Hewlett-Packard Development Company, L.P.	Commercial	Web and Federated Single Sign-On Solution
Imprivata OneSign[12]	Imprivata	Commercial	Enterprise single sign-on and authentication
Janrain Federate SSO[13]	Janrain	Commercial	Social and conventional user SSO
JBoss SSO	JBoss	Free Software	Federated Single Sign-on
JOSSO	JOSSO	Free Software	Open Source Single Sign-On Server
OX[14]	Gluu	Free Software	Open Source Single Sign-On + Trust Management
Gluu[15]	Gluu	On Demand Software	Single Sign-On + Trust Management
JsonSSO[16]	NimbusDS	Commercial	Sign-On for Ajax and cross-domain applications
Kerberos	M.I.T.	Protocol	Computer network authentication protocol
LTPA	IBM	Commercial
myOneLogin	VMware Inc.	Commercial	Cloud single sign-on
Numina Application Framework	Numina Solutions	Commercial	Single sign-on system for Windows
OneLogin	OneLogin Inc.	Commercial and Free	Single sign-on with SAML and Active Directory integration
Okta	Okta,Inc.	Commercial	On-demand identity and access management service in the cloud
OpenAM	ForgeRock	Free Software	Access management, entitlements and federation server platform
OpenASelect[17]	Alfa Ariss	Commercial and Free
Oracle Access Manager[18]	Oracle	Commercial
Oracle ESSO (formally Passlogix v-GO)[19]	Oracle	Commercial
PingFederate[20]	Ping Identity	Commercial
PortalProtect[21]	Asseco Denmark	Commercial
Pubcookie	University of Washington	Protocol
SAML	OASIS	Protocol	XML-based open standard protocol
Secure Network Communications	SAP	Commercial	Authorization layer in SAP software system
Shibboleth	Shibboleth	Free Software	SAML-based open source access control
Tivoli Identity Manager	IBM	Commercial	Identity life-cycle management product
Security Access Manager for Enterprise Single Sign-On	IBM	Commercial	Enterprise Single Sign-On, Strong Authentication, Password Management product
Tools4Ever SSO Manager[22]	Tools4Ever	Commercial
Ubuntu Single Sign On	Canonical Ltd.	Commercial	OpenID-based SSO for Launchpad and Ubuntu services
Microsoft account	Microsoft	Free and Commercial (Microsoft is now attracting new websites to use system)	Microsoft single sign-on web service
ZXID	ZXID	Free Software	Reference Implementation of TAS3 security
SmartSignin	www.smartsignin.com	Free, Professional, and Enterprise versions	Web/Cloud SSO, Password Management, Two-factor authentication, & Identity & Access Management application