Versiontracker which is always a great resource for Mac software shows 50 results for "word processor": freeware, shareware and commercial. Search for "Text Editor" and there are almost 80 more.
Macs come with TextEdit, which can do more than just writing words. There are two settings: plain and rich text. In Plain text it is straight-forward enough to write an HTML file.
In Rich Text there are more features, and it is a basic word processor: tables, lists and text formatting are all within its compass; and it has the advantage that images are easily dragged into a page. If these are too large, however, there may be a significant delay, so a user should be prepared to save a smaller copy in such cases.
With its click and drag facilities Text Edit has increased flexibility and we can also include applications. Click on the icon on a page and any application will open. This applies to third party programs as well as Apple-written software.
TextEdit is able to access the Apple installed fonts and using Thai, as well as scores of other languages, is easy. Files are saved in rich text format (RTF), rich text format directory (RTFD) when other files are included, as well as DOC, ODT, DOCX, Word 2003 XML format, plus HTML. It also opens these files.
For writing web pages and for basic text, I use the free text editor, Text Wrangler from Bare Bones Software which now replaces my version of BBEdit from the same company. BBEdit is considered to be a professional text editor and has several more features that are valuable for programmers and the like.
TextWrangler itself has several useful, albeit basic, functions: I especially like Find and Replace, for example. All my columns and 99% of my web pages are written with this. It can also use the Thai fonts. It will do footnotes.
For more sophistication, I have Apple's Pages and NeoOffice. The latter is an Open Source suite which has spreadsheet, presentation and drawing software along with the Word Processor, which has a full set of tools. It is sometimes a little slow. It saves and opens files in 22 formats including Microsoft types and HTML. NeoOffice has the Aqua interface and does not need the X11 window to be installed.
There is also Open Office, now in a beta version that also now does not need X11. Another development of the Open Source suite is Open OS X Office which was part of a larger collection of software that may suit some. The word processor is called AbiWord.
Pages is part of Apple's iWork suite (including the spreadsheet Numbers and the presentation application, Keynote), this is a highly flexible application that handles Thai and allows the creation of some stylish work. There are templates for word processing, which includes letters, envelopes and reports, and for Page Layout with newsletters, posters and business cards. Most use a simple click and drag of images (or other files) from the media browser displayed plus the addition of our text.
Bean is a delightful, free text editor with a few frills. It advertises itself as not a replacement for Word, although for most of us it is one of several applications that does just that. It handles Thai fonts. The toolbar links to the installed dictionary which provides a definition without the need to highlight a word: with the cursor at the word, that is enough. The Inspector allows some quick adjustments and includes a useful slider to change font size.
Nisus Writer Pro was in beta [now updated to version 1.1] and looks similar to Bean with a more formal interface. An examination reveals that this is a feature-rich application and would appear to be aimed at those who need quality tools. A drawer reveals many of these and it is ready to work in several languages (the keyboards need to be included in System Preferences).
Keys can be tuned to the user's own working style and these are added or changed in the comprehensive preferences panel. It saves in eleven file types with RTF as default. The specific Word format was not specified, but a file appeared with the DOC extension.
Its sister, Nisus Writer Express, has a slightly simpler set of features although has much of the look and feel of the Pro application. Both are available as 15-day demos and are priced at $79 and $45.
In the past I have also mentioned Think Free Office, a suite that works well with OS X and also Mellel, a word processor from Israel, on a par with Nisus Writer Pro, that is well-suited to higher level academic writing, with some of the attributes of the Open Source LaTex. The Mac version of LaTex is MacTex.
Already installed on Macs and accessible from the Terminal window are the Unix emacs, pico and Vim.