TLA Systems has updated PCalc (www.pcalc.com), for Mac OS X, to version 4.2. It sports several improvements, including a calculator widget.
PCalc is a scientific calculator with support for hexadecimal, octal and binary calculations, as well as an RPN mode, parentheses, programmable functions, and an extensive set of unit conversions. Version 4.2 offers an advanced layout with more of the functionality of the main application. The widget also now supports keyboard shortcuts for all operations.
This is a free upgrade for existing users. For new users the cost is US$9.99. PCalc requires OS X 10.8 and later. It’s available at the product website and the Mac App Store.