Ultimate++ is a C++ cross-platform rapid application development suite. It includes a set of libraries (GUI, SQL, etc..), and an integrated development environment.
Rapid development is achieved by the smart and aggressive use of C++ rather than through fancy code generators. In this respect, U++ competes with popular scripting languages while preserving C/C++ runtime characteristics.

The U++ integrated development environment, TheIDE, introduces modular concepts to C++ programming. It features BLITZ-build technology to speedup C++ rebuilds up to 4 times, Visual designers for U++ libraries, Topic++ system for documenting code and creating rich text resources for applications (like help and code documentation) and Assist++ - a powerful C++ code analyzer that provides features like code completion, navigation and transformation.
TheIDE can work with GCC, MinGW and Visual C++ 7.1 or 8.0 compilers (including free Visual C++ Toolkit 2003 and Visual C++ 2005 Express Edition) and contains a full featured debugger. TheIDE can also be used to develop non-U++ applications.
U++ distributions combine U++ with 3rd party tools like MinGW compiler or SDL library to provide an instant development platform.
What you can get with the Ultimate++ download in plain English
Very effective C++ library for cross-platform development in source form.
A good integrated development environment, designed for developing large C++ applications.
You can use both, or you can use whichever you need.