pearCalc

pearCalc is a freeware calculator, application-launcher and text replacement tool that uses incredibly little space on your screen.

As calculator it provides a broad range of operations (i.e., -, *, /, sin, cos, tan, log, %, mod, ^, sqrt...). Of course it also handles parenthesis correctly.
The application-launcher function lets you launch applications simply by entering an application name. pearCalc can also launch web pages with your favorite browser and generate new emails with your favorite email-app.