Freeware Descriptions:
Calculator++ is a cross-platform, arbitrary-precision, customizable, multifunction, scientific calculator. Using Calculator++, you can perform any of the customary handheld or online calculator operations, and many more.
Here is complete features (taken from authors site):
While it serves as an excellent replacement for your operating system´s built-in calculator, it also offers many powerful features that are not available together in any other handheld or computer-based calculator. Calculator++ supports over 25,000 units for conversion in an ever growing list of categories and units. Scientists, engineers, programmers, and students will find it a simple to use, yet powerful, tool.
Calculator++ is written entirely in Java, so you can use it on the platform of your choice.
Requires Java Runtime Environment (JRE) 6 or above.

File Size / OS:
- 1.63 MB / Windows 9x - ME - 2000 - NT - XP - 2003 - Vista
Download Calculator++ 1.0.1.75:
The latest version as of Jun 3, 2009 is 1.0.5 (Build 79). They should update this web site.