Linux is the best operating system, period. Unfortunately, this well kept secret means you'll be forced to work with some other operating systems along the way. Schools (including my own) have latched onto the Ipad as the tool of choice. So it's good to know what apps are out there. I've selected the free calculator apps that I like best. I don't include the Sage app because it requires you to be online and the input is clumsy on tablets. My calculator choices are all scientific calculators because a plain vanilla calculator won't be able to handle a variety of basic high school math calculations. Here's the list of the best calculator apps out there.

4. Free Graphing Calculator is a good quick-I-need-the-answer-to-this-simple-calculation calculator. Although you have the ability to for more complicated calculations, such as hyperbolic sine, it's cumbersome to use. On the positive side, it allows you graph multiple 2d functions simultaneously and gives you access to mathematical results. Can't remember that half angle formula? Not to worry, this calculator has it.

3. HiCalcHD comes in next but the annoying reminders when you start it up detract from the experience. A large variety of functions are readily available, including trig functions, log functions, exponentials, factorials, combinations, integrals, and series. Some of the nonstandard calculations tell you how to properly input the calculation you are working on (such as the definite integral) while you're typing. You can even set the calculator to work in RPN (reverse Polish notation). Great calculator but those reminders....

2. Calculator $latex \infty$ is free for now, so download it ASAP. No really. Stop reading and download it now. This calculator has everything HiCalcHD has and even lets you input fractions and convert the resulting answer to a fraction.

1. Halcyon Calc Lite takes top spot, though it is definitely not for everyone. Pictured at the top of this post, it's modeled after the HP28S calculator: a calculator that was cutting edge when I bought it over 25 years ago (!):

Since I own the HP28S and am familiar with RPN notation it was pretty easy for me to find my way around. There is more functionality here than any of the other calculator apps I've mentioned, probably more than a typical person will use. Unfortunately, someone new to this type of calculator will almost certainly struggle.

I do have one complaint, though. After graphing a function I was unable to figure out how to get back to the calculator. I couldn't find instructions anywhere. When I exited the app and opened it up again, I was left looking at the graph I created. Eventually I just deleted the app and installed it again. Whether that's a bug, lack of documentation, or a feature meant for the paid version, I have no idea. Note there's a demo video on their website, if you're curious.

If you need an excellent scientific calculator then Halcyon Calc Lite (for people who want RPN) and Calculator $latex \infty$ (for people who don't) are the best free apps out there.