Both Rational Robot and Rational Functional Tester are Functional testing tools,The Scripting Language for Rational Robot is SQA Basic (Similar to VB) and the Scripting language for RFT is Java/.net.
Rational Robot can be used to test web application for that we need to add suitable Enablers(Like add-in in winrunner) to support the Application
Rational Robot can be used for Functional Testing(GUI scripting) and for Performance testing (VU scripting),where as RFT is only a functional tester