These companies differ from pure on-demand (SaaS) providers in that their products are more than software. They also tend to be larger, more established companies such as Rearden Commerce or Morgan Stanley that have multiple federated identity use cases. These types of companies use PingFederate in a hybrid manner. They support both incoming Single Sign-On for their customers, as well as outgoing SSO for their employees.
PingFederate is a particularly good choice for this use case because pricing is connection-based, versus seat-based, the model most common with identity management products designed to manage employee identities.