Editing Japanese Text Documents
Once you have enabled Japanese input on your Mac (as described on the first page of this site), you can write Japanese documents with compatible text editing software. Here a few options that work well for writing in Japanese.
TextEdit. You can start off with this simple but powerful text editor that comes with OS X. TextEdit has the very useful ability to open and save files in a range of different encodings.
Microsoft Word includes a lineup of features for working in Japanese, like vertical text, "ruby" or furigana and special search options and text formatting not used in English. To activate these features in Word or other Office programs, you need to use a program called the Microsoft Language Register. It should be in the Microsoft Office folder under "Additional Tools"; just open the application and it will give you instructions.
iText Express from LightWay is a free Japanese word processor with English menus and documentation. It combines the simplicity of Apple's TextEdit with some advanced Japanese support, including vertical text and Japanese manuscript (genkô yôshi) layout. The developer also produces more powerful paid versions of the program, iTextPro and LightWayText) with features like Ruby/Furigana. iText Express and Pro are available on the App Store.
The word processing programs below may not have the Japanese features of MS Word or iText, but they do have a reputation for supporting Japanese input along with a wide range of other non-roman scripts, including right-to-left scripts like Arabic and Hebrew.
Mellel is a word processor that can combine and format many different non-roman languages.
Nisus Writer was one of the first word processors to support Japanese on the Mac.
Pages is Apple's Word Processing and page layout software. I've used this to combine Russian, Greek, Chinese, Japanese, Arabic, and Hebrew text in a single document when creating posters for our Comparative Literature program.
I don't do graphic design work, so I mostly make do with the Japanese fonts distributed with OS X. For those who want something more, here is a starting point:
Wazu has an excellent list of free unicode fonts available on the web, including links to many Japanese fonts you can download. The site is in English.
Hakushu Shotai also has some interesting Japanese fonts you can download free. The site is in Japanese, and the free fonts come with some license restrictions, and generally include only a subset of the most common kanji.