Calculator extends the 4 function calculator. It's simple and uncluttered, but gives you access to advanced functions with a swipe. Graphing, matrices, base conversion, and more are at your finger tips, and only when you need them. Calculator also has a widget, a floating calculator, and 7 (and counting) alternative themes. It also runs on Google Glass.
Calculator was started in June 2012, by Will (myself) and Sean, as developer and designer respectfully. Over 4 months, we added basic support for matrices, graphing, and history, and in October 2012, Calculator became officially included within CyanogenMod (and most custom ROMs soon thereafter). In January 2013, Nick joined the endeavor, redesigning the graph page, hex page, and has, more recently, created all of the available themes. In September 2013, Rudy joined for a short time and greatly improved the matrix logic, adding support for functions, order of operations, and more. And, of course, the vast language support has all been thanks to users. The calculator has been, since its start, open source, and is always looking for more helping hands.
Because the app is intended as a full replacement, it's recommended that you disable your default calculator. Go into Settings, Apps, and you will be able to disable it where you would normally find Uninstall (Requires Android 4.1+).
The source code can be downloaded here: https://github.com/Xlythe/android_packages_apps_Calculator/tree/ics