GS-Calc 10 ($20, 30-day free trial) is an inexpensive spreadsheet program that isn't an Excel clone. It also has some imperfections that are at least partially mitigated by the low price.

Developer Citadel 5 packs GS-Calc full of interesting features, including a large work area (4094 columns by 12 million rows),  pivot tables, robust charting, and a nice interface for dealing with multiple worksheets in a single project.

GS-Calc has an unusual, and welcome, take on multipage spreadsheets.

Rather than a row of tabs along the bottom to handle multiple sheets, which becomes problematic when a workbook grows beyond four or five pages, GS-Calc offers a hierarchical, folder-based view supporting multiple levels of folders. This makes it  easier to create a workbook consisting of many smaller, more-focused sheets, a boon to navigation and debugging.

GS-Calc also offers an interesting method of generating multiple values.

A single formula can fill several cells with calculated values. These "array formulas" work with most of GS-Calc's functions. For example, entering "=SQRT(4)+{1;2;3;4;5}" will produce the numbers 3 through 7, in five cells, beginning with the one in which the formula was entered. If the data in one of the "generated" cells is overwritten or changed, it is refreshed as soon as the worksheet recalculates itself.

By using references to worksheet ranges as part of the array, an array formula in a single cell can fill many cells with data. It's much easier to correct errors in that single formula than to do so in many cells, even with features like Excel's auto-copy to make the job easier.

GS-Calc is loaded with functionality, but hides the full list and all descriptions in the dialog box you can use to enter a function. The description and examples contained for each function in this dialog is thorough, but this is the kind of information that should be in the Help file. Having it in the dialog is a very helpful addition to having it in the Help, but it isn't a replacement for it.

Version 10 of GS-Calc corrects one of the flaws of Version 9: The screen redraw and interface responsiveness is much better, without the flicker effect sometimes seen before. It still retains some of the interface oddities, such as numerical overflow going to the left by default, rather than the right, or the workable, though non-standard, use of the Ctrl key to select cell addresses while entering a formula.

Other improvements to GS-Calc 10 include a compressed, proprietary save format, in addition to the ODF (Open Document) format, and the ability to add a note file to each document, which can be displayed in the bottom or left panes. The notes are linked to the entire document, not to any individual sheet or cell. Cell deletion has been made more flexible, as well. These are "quality of life" improvements, small changes that enhance the application without massively changing the user experience or basic functionality.

GS-Calc also features support for pivot tables, allowing for the easy creation of summary reports and breaking down data into various categories. Charting, both 2-D and 3-D, is also supported. While it doesn't contain any revolutionary breakthroughs, the charting function has options for user control and styling of the information presented, and the interface is generally clear despite there being many possible values to adjust.

GS-Calc offers a great deal of functionality for a very low price, and version 10 is an incremental upgrade. Nothing in version 10 makes GS-Calc radically different from version 9, but it shows a commitment to frequent improvements and fixes.

GS-Calc is especially useful for working with data best broken into multiple pieces, but it does have the capacity to handle large quantities of information as well, making it a good tool to grow with. The 30-day trial should be sufficient to evaluate its performance on whatever tasks you might need it for.