Mac OS X has a pretty nice calculator bundled that is sufficient for daily purposes. Well, actually there are many. There is a dashboard widget, and Spotlight can do calculations. For more advanced things, you can use the Calculator app. Its scientific view met my needs… until now.
I needed to calculate some base-2 logarithms. Turns out the Mac OS X calculator can only do base-10 and natural logs. So I went to Google and among the first results, found a very nifty Console Calculator. It has a nice view as a widget.
It supports logarithms of arbitrary base, plus a host of other advanced functions. Plus a very nice property is that if you need to do a complicated calculation, you can just paste it in as an expression (as you see above) and get a result, without needing to go through the whole sequence by hand.
The only missing feature? Being able to copy-paste the result from it into another place. Right now you need to type it, which is not too bad, but copy would be a bit more convenient.
MATH NERD UPDATE: I just realized that log2(x) = log(x) / log(2). So in theory, you could do all this with a calculator still that can just do base-10 or base-e logarithms, with an extra division involved. But being able to do log with the correct base right away is much more convenient ;)