Palm Fiction is a free, open source viewer from a Russian programmer for a variety of Palm documents. Palm Fiction can read FB2 files, Palm "doc" files or zTXT files in RAM or on a card. It can also display plain ASCII text files, Rich Text Format files and Word documents (which it renders as plain text), and files in Zip and gz archives stored on a card.
Palm Fiction can navigate the file system on a card, and documents read with it can be stored wherever you like.
It's skinnable, with skins available for low resolution (160x160) and high resolution (320x320 and 320x480) PalmOS screens, and is highly configurable, supporting custom fonts, display arrangement, and toolbar buttons. It comes with a variety of font sizes, which allows you to choose the most comfortable size for your eyes. It also allows an easy toggle to/from full screen mode to maximize your reading area.
The home page is in Russian, but the program is available in English, French, Spanish, German, and Bulgarian as well as Russian. There are no docs, but configuration is fairly simple with a little experimentation.
Palm Fiction supports bookmarks, but category support is broken. The author suggests using sub-directories on a card to organize documents read with it.
There are support forums in English and Russian. (The author reads English well, but writes it less well.)
Palm Fiction is written in a PalmOS port of Pascal, and is the only major application I've seen for Palm devices in that language.
It may be found here: http://palmfiction.sourceforge.net