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Spreadsheet applications like Microsoft Excel and OpenOffice.org Calc are extremely powerful. That's great for complicated financial and business-related calculations, but sometimes, I simply want to add up a list of expenses or the measurements for a home-improvement project...and I don't want to play with parentheses and colons to do it. For those cases, OpalCalc is just the ticket.

OpalCalc makes quick work of day-to-day calculations, even if they include currency conversions.At first glance, OpalCalc looks like a notepad application. There are no rows, columns, or any of the other traditional spreadsheet interface elements. The resemblance to notepad is not complete: the text editing area is vertically split. Write your calculations on the left, and the magic happens on the right.

The idea behind OpalCalc is not entirely original, and the author credits several applications that provided inspiration, such as Console Calculator, Speq, and Soulver. Specifically, Soulver bears a striking resemblance to OpalCalc, but alas for Windows users, its most recent versions are Mac and iOS only.

It is very easy to use OpalCalc for calculating the budget for an outing, for example. Just begin listing all of the expenses you want to budget for, much like you would on a napkin: so-and-so for breakfast, so-and-so for tickets, etc. As you list the items, you'll see the numbers you've included in every line extracted on the right. Once you're done listing all of the expense items, simply type the word "total" in a line of its own. OpalCalc will add up all the numbers and display the total.

That is just scratching the surface of what OpalCalc can do. The application features a built-in currency converter, pulling live currency rates off the Internet. So, for example, if you have a list of prices in US dollars and want to know how much they all add up to in Canadian dollars, simply append the words "as CAD" to the line that says "total".

OpalCalc lets you set up your own variables: for example, you could have a variable called "CostPerPerson" (no spaces are allowed in variable names). Then, if you have five people in your party, you can simply write something like "5 * CostPerPerson", and instantly see the result on the right. You can also set up your own functions (although if you find yourself needing those, perhaps it's time for a real spreadsheet).

Much like a spreadsheet, all calculations in OpalCalc are dynamic and instant. As you change a single number in your document, all other numbers affected by it will instantly update to reflect the change. This makes it very easy to play with the numbers and look at different scenarios.

OpalCalc comes in handy for home improvement projects, too: it features an extensive unit conversion system, and understands both Imperial and metric measurements. For example, you could use it to calculate the surface area of a room you'd like to paint, and then divide it by the coverage area of a single bucket of paint, and multiply that by the cost of the bucket, ending up with the cost of paint for that room.

Since OpalCalc is so open-ended, it is not without its quirks; Its natural language parser makes it easy to get things wrong. For example, the keyword it expects for currency conversion is "as". If you use the word "in", such as "5 USD in CAD", OpalCalc will not understand. So, intuitive as it may seem at first, you may still find yourself resorting to the online help and trying to memorize the syntax.

Another unique aspect of OpalCalc is its pricing model. OpalCalc is donationware: You can try it for free with documents up to five lines long, but if you wish to use it for longer documents, you need to donate. It's called a donation, rather than a fee, because you get to set your own price. The OpalCalc website contains a textbox letting you enter any amount of money (in GBP or US dollars). This can be as little as a few cents, although the developer recommends a donation of $5-$25.

For simple day-to-day use, OpalCalc feels more natural and "human" than Excel, at least for me. By being different and targeting a narrower use case than traditional spreadsheets, OpalCalc has managed to carve itself a uniquely valuable niche.

--Erez Zukerman