REALbasic
REALbasic is an implementation of BASIC.
Other implementations of BASIC.
REALbasic is an example of an Integrated Development Environment, a class of software which typically combines enhanced editing and debugging features.
REALbasic is an example of a compiler. You may find the programming tasks that have been solved using it here.
REALbasic (or RB) is a BASIC compiler for Windows, Mac OS, and Linux, made by REAL Software, Inc. It has its own IDE, and projects are saved to a proprietary binary format. Unlike most BASICs, REALbasic is heavily object-oriented.
REALbasic is not compatible with other BASICs, for the most part; examples from other BASICs usually have to be completely rewritten to work in RB.
The Wikipedia article has lots of information about REALbasic's history, capabilities, and features.