Tapbots have today launched a Mac version of their Calcbot app. Priced at $4.99, Calcbot for Mac is a good replacement for the default OS X calculator if you want a calculator with a few more bells and whistles but don't necessarily need something as advanced as PCalc. Calcbot comes with a Basic and Scientific calculator, as well as an in-built unit converter.
Just like Tapbots' terrific Twitter client, Tweetbot, Calcbot is beautiful and delightful to use. It looks great and fits perfectly within the new look of OS X Yosemite with a clean, sharp look and touches of translucency. Calcbot for Mac also has Tapbots' trademark touch of elegantly smooth transitions (without being superfluous) such as when you switch from Basic to Scientific mode and vice versa. When you make the switch, the extra buttons for the Scientific mode gracefully slide out from under the basic calculator. Try the same with Apple's own calculator app and you'll notice that there is no graceful transition but an abrupt switch in window size.
A built-in conversion calculator is accessible by tapping the conversion icon in the top-right corner of Calcbot. From there you can convert between virtually any kind of unit you can think of by tapping the icon on the far left of the conversion box (go to Calcbot's preferences to enable them all). By default, you will be modifying the unit on the left, but by tapping the centre arrow you can flip the units and convert the other way. Tapping on one of the units will let you swap it out with another.
Finally, it is worth noting that Calcbot for Mac also has a 'tape' that slides out on the right which contains a history of calculations and any favorited calculations. Click on any of these calculations in the tape and you can copy them for use elsewhere or re-use the result or expression in another calculation. Also neat is the ability to email the entire tape which is accessible from the Settings cog on the tape.
Calcbot is available from the Mac App Store for $4.99. If you do end up buying it, be sure to check out the difference in the animation of the buttons being pressed when you click with a trackpad versus tapping with a trackpad – it's an impressive level of attention to detail.