Back in the v9 days, WebSpeed had its own version numbers (3.1, etc.) and its own product license. As Stefan said, in v10 and v11 the runtime portion of WebSpeed is in the AppServer products, Basic or Enterprise. But you can't compile WebSpeed code with only AppServer installed as you'll be missing the required e4gl-gen.r compilation program.
WebSpeed Workshop includes the %DLC%\gui\webutil library with this program. It is a separately-licensed development product and is Windows-only. It also has some functionality our web developers like, e.g. a browser UI to browse file systems, view propath, run scratch programs, etc. It's nothing you can't do in PDSOE, in my opinion, but I'm certainly no WebSpeed expert; I might be missing something.
If you're in a Windows environment, you can compile WebSpeed code with either a WebSpeed Workshop or 4GL Development System license. In Unix, you need 4GL Development System.
Take care in choosing the license model for your WebSpeed-specific AppServers. If your web application end users are classified as "unknown users" then you have to choose the Access Agent model for both front-end (AppServer Basic or Enterprise) and back-end (Workgroup or Enterprise RDBMS). Unlike the Named User or Registered Client models, Access Agent is a single-server license model and it is also more expensive per seat than the others. But this latter point makes sense as it is intended for many-to-one usage.
With regard to the RDBMS license, note that a given application might require more than one. For example if I had a an application with both a GUI front-end and a web UI, I might have something like this for a single environment:
Enterprise RDBMS, 100 users, Named User (NBP) (GUI app, server side)
Client Networking, 100 users, Named User (NBP) (GUI app, client side)
Enterprise RDBMS, 5 agents, Access Agent (AAP) (WebSpeed app, server side)*
Enterprise AppServer, 5 agents, Access Agent (AAP) (WebSpeed app, client side)
*this second RDBMS license is sometimes referred to as a "paper license" as it isn't installed on the server; it is just purchased for compliance.