When creating or editing a Salesforce User, there is a picklist field that lets you assign a specific User License. In my Developer org, there are several options, two of which are confusing to me: Salesforce and Salesforce Platform.
What is the difference between these two license types?
The main difference is the price and the objects you can access. The following help page has more detail:
http://login.salesforce.com/help/doc/en/users_understanding_license_types.htm
Authenticated Web Site is the Platform Portal and has read and create access on ideas and questions and answers, and read-only access to documents, knowledge, price books, and products.
The High Volume Portal is the Service Cloud Portal and has access to accounts, assets, cases, contacts, custom objects, documents, ideas, and questions
The following Venn diagram by Steven Herod shows the relationships between the various license types:
I believe those are the differences. Think of platform as more of a license of you're getting the cloud framework/platform to build your instance or apps. You get some standard items like reports, dashboards, documents, accounts and contacts...but everything else you want you have to build out. Also in a multi-license environment you may have both standard CRM sales cloud licenses and also platform licenses....with each having specific use cases (sales cloud license for sales and maybe services, platform for your core administration departments).
In regards to your last item, it may be because it was rebranded as force.com license.
Best Answer
My thanks to @mattandneil, who found this Salesforce.com Article for me to reference.
Salesforce licenses are designed for users who require full access to standard CRM and Force.com AppExchange apps. CRM apps are anything that requires access to Standard Objects like...
Salesforce Platform licenses are designed for users who only need access to custom apps, and NOT the standard CRM functionality. Salesforce Platform users DO have access to the "core" Salesforce Standard Objects and functionality, like...
So, if a user only needs to access custom Force.com or AppExchange apps, it's OK to assign them a Salesforce Platform license. On the other hand, if a user needs access to any CRM functionality (eg Sales or Service Cloud), they must be assigned a Salesforce license.