Excalibur

Excalibur is a RPN calculator (Reverse Polish Notation) designed for users who work in specialized domains, such as Computer Science, Physics or Statistics. It can be used by students, for instance.
This is a portable app, so Excalibur does not come with a setup pack. In other words, you can save the tool on a removable device (like a USB flash drive) and directly run its executable file on any computer.
More importantly, no leftover items can be found in the Windows Registry or on the hard drive after program removal. Moreover, you can carry Excalibur with you whenever you're on the move.
The interface of the program is based on a standard window with a familiar layout. So, it is possible to list functions according to their bank. For instance, when it comes to scientific functions, you can use trigonometric tools  (e.g. sine, cosine, tangent), fractions and logarithms.
On top of that, you can copy the entire stack, view system usage statistics and define a custom set of functions, as well as configure program settings (e.g. angle mode, numpad lock, comma format, footprint size, tax constant).
The software program runs on a very low amount of CPU and system memory, so it is not a concern to the computer's resources. It has a good response time and includes a help file. We have not come across any problems in our tests, since Excalibur did not freeze, crash or pop up error dialogs. All in all, this app should please all users who require a full-featured RPN calculator. Unfortunately, no recent updates have been made.