I think what you've done is cool, but lets be clear that this is not really a testing tool, per se. It's just an interface that is compatible with several browser automation tools.
Cucumber, FitNesse, and robotframework are testing frameworks. xUnit frameworks can act as one. If you look at Robot's architecture (http://robotframework.googlecode.com/hg/doc/userguide/RobotF...) what you've written would occupy the "Test Tools" tier.
A nit pick - 'acceptance testing' really refers to the purpose of the test, whether it's automated or manual. Splinter is a test tool - it would work equally well for regression testing, smoke testing, etc.
Cucumber, FitNesse, and robotframework are testing frameworks. xUnit frameworks can act as one. If you look at Robot's architecture (http://robotframework.googlecode.com/hg/doc/userguide/RobotF...) what you've written would occupy the "Test Tools" tier.
A nit pick - 'acceptance testing' really refers to the purpose of the test, whether it's automated or manual. Splinter is a test tool - it would work equally well for regression testing, smoke testing, etc.