Our company uses Servoy for rapid application development. It is a 4GL environment, that can target web-applications running in Tomcat as well as Java applications, all from the same program.
While it is standards based, some aspects of the generated code are proprietary, which couples those applications to the Servoy environment and tools.
Is Servoy truly unique in terms of the feature set that it provides, or are there alternatives that provide similar feature set, but without the lockin?
With Servoy specifically, I would say no - at this stage.
You probably already know that Servoy isn't really unique in terms of the tools it uses to get the job done (hibernate and Rhino etc), but I would say that the style of development that you need to use for Servoy is fairly unique. I mean this in the sense that your form variables directly link to precached database results, leaving little or no need for OOP.
I believe until their documentation gets a whole lot better and they actually start gaining more popularity, then there may be a few more competitors or variations popping up.
Here is a list of other RAD development tools that are out there in case you are curious - http://en.wikipedia.org/wiki/List_of_graphical_user_interface_builders_and_rapid_application_development_tools
Intellimaker offers a similar feature set. You might look into ThinkCap JX too.
