Why not OpenOffice.org? The OpenOffice.org project does provide a build for OS X, but it's dependent on X11, doesn't support copy and paste from other applications the way that NeoOffice does, and generally isn't as well integrated into Mac OS X.
For example, OpenOffice.org menus (File, Edit, etc.) are located within the application windows, whereas NeoOffice supports the traditional Mac OS X design and uses the traditional Mac menu bar at the top of the screen. Copy and paste works, but only if you manually copy and paste the text -- with NeoOffice, you can simply highlight text in another application (say, Firefox) and drag it to an open document.
Fonts look much better in NeoOffice than in OpenOffice.org out of the box, because NeoOffice enjoys native support for Mac OS X fonts. OpenOffice.org's fonts look jagged and a bit clunky -- a reminder of the bad old days before Linux had decent font support.
The minimum requirements for NeoOffice are Mac OS X 10.3, 256MB of RAM, and at least 400MB of free disk space. NeoOffice builds do not run natively on Apple's Intel-based Macs, though the project is projecting an alpha build for Intel-based Macs sometime this summer. I installed NeoOffice on a 1.8GHz G5 iMac with 1GB of RAM running Mac OS X 10.4.5.
NeoOffice installation is typical of other software on Mac OS X. Once you download and mount the NeoOffice disk image, you only need to double-click on the NeoOffice package (.pkg) file and walk through the steps to install it. Not quite as simple as "drag the icon to the Application folder," which is used by OpenOffice.org, but simple enough. It will probably take you longer to download NeoOffice than it will to install it.
After the installation, I fired up NeoOffice and started by testing out Writer. For all intents and purposes, I didn't see any difference between NeoOffice Writer and Writer in the 1.x versions of OpenOffice.org. If you've used OpenOffice.org 1.x, then you'll feel right at home using NeoOffice.
In addition to writing a few letters using NeoOffice, I tried it out using some Microsoft Word documents I've received from PR folks over the years. For the most part, things looked fine in NeoOffice -- a few elements might not be aligned properly, or there may have been other cosmetic issues, but the documents were usable in NeoOffice.
I found that NeoOffice isn't quite as drag-and-drop friendly as some other Mac applications. For example, while it's possible to copy and paste text into NeoOffice Writer using drag and drop from other Mac OS X applications, the same isn't true for images. This isn't a big deal, but it does illustrate that NeoOffice still has a little way to go before it's fully integrated into Mac OS X.
Next, I spent some time playing with NeoOffice Calc. I created a few sample spreadsheets and imported spreadsheets in Microsoft Excel and comma-separated value (CSV) formats. NeoOffice did fine with Excel files with basic formulas (such as an expense spreadsheet) and CSV files. It still shares the OpenOffice.org 1.x row limit; I tried to open a CSV file with more than 65,000 rows, but NeoOffice truncated the file at 32,000 rows. For more reasonably sized spreadsheets, however, NeoOffice was just fine.
To test NeoOffice Impress, I created a presentation for my Linux User Group, and tried out a few PowerPoint presentations I have received from PR folks. NeoOffice comes with only a handful of templates, but they're relatively nice. Though I prefer the new OOo 2.0 layout for Impress, NeoOffice is still fine.
The PowerPoint presentations looked much better in NeoOffice than in OOo 2.0 for Mac OS X, thanks to the better font support. If you're going to be giving a lot of presentations using a Mac, you might want to go with NeoOffice.
NeoOffice includes the Draw component from OpenOffice.org, but I didn't spend much time using it. If I want to create vector graphics images, I'll use Inkscape, which provides a native Mac OS X version. NeoOffice also includes OpenOffice.org's formula editor, but doesn't include the database application Base, which debuted in OpenOffice.org 2.0.
An interesting feature of NeoOffice is NeoLight, a plugin that allows OS X's Spotlight to index content and metadata from files in ODF and OpenOffice.org formats. This means that if you're using NeoOffice or OpenOffice.org with the NeoLight application, Spotlight will work with all of your files.
Compared to OpenOffice.org and other Mac apps, I found NeoOffice to be a little sluggish on the test Mac. For example, it took NeoOffice a few seconds more than OpenOffice.org to open an Impress document. It took about 11 seconds for NeoOffice to launch, while OpenOffice.org would be ready to use in about five seconds, as long as X11 for Mac OS X was already running. Opening new documents is also much faster in OpenOffice.org than NeoOffice. Granted, I'm talking about a difference of only a few seconds, so if you use your office suite infrequently, the performance difference really shouldn't be a big factor.
NeoOffice proved to be stable while I was testing it, though I was able to stymie it with a particularly large Word doc of the King James Bible. Oddly enough, OpenOffice.org 2.0 had no problem at all opening the file in less than a minute, while NeoOffice took the better part of 30 minutes to do so. Also, while OpenOffice.org handled Greek characters in the file with no problem, NeoOffice had some trouble with non-Latin characters. After saving the file in the native format, NeoOffice had less trouble with it and managed to open it in a few minutes.
NeoOffice has limited support for the Open Document Format (ODF). It will open documents created in OpenDocument, but will not save or create new documents in that format. If read/write support for ODF is important to you, you'll need to look at running OpenOffice.org 2.0 for the Mac.
Finally, NeoOffice uses the traditional OpenOffice.org open dialog rather than the standard Mac OS X open dialog. To put it charitably, the NeoOffice dialog is clunky compared to the Mac OS X file dialog or the current GNOME/KDE dialogs.
For Mac users, NeoOffice may be the best free suite available. It lacks some of the features you'd find in OpenOffice.org 2.0, and still sports the old OOo interface, but it makes up for its shortcomings somewhat by being better integrated with Mac OS X.
For most users, the choice between OOo and NeoOffice is likely come down to personal preference. Die-hard Mac users will probably prefer NeoOffice, even if it lacks a few features that are available in OpenOffice.org 2.0. Linux and *nix users who use Mac OS X as an additional OS will probably want to stick with OpenOffice.org 2.0, if for no other reason than to be in sync with their other systems.
NeoOffice is a great alternative for users who want to have an office suite, but don't want to shell out for Microsoft Office or Apple's iWork applications. It lacks some of the functionality of Microsoft Office, but it has all of the basics well covered. I didn't find NeoOffice lacking in features or usability.
Since NeoOffice is open source software, available under the GNU General Public License (GPL), there's no real risk to trying it out, so don't just take my word for it. Download NeoOffice and see if it fits your needs.