Can you recommend an editor for both iOS and Mac OS X designed for writers? Is there an editor designed specifically for writers of short prose? Currently I am using Microsoft Word and it is very heavy weight. 

Large technical reports need indices, chapters, heavy formatting (provided by tools like Word and InDesign), and programmers desire all sorts of code hooks, definition lookups, and integration with other tools like Xcode or code control tools.

I want a tool for putting out prose and haven't found good solutions for this need.

Better for writers means:


fast - especially on older macs without SSD or large amounts of RAM
lightweight in feel as well as in visual impact


Ideally this tool should be available for both Mac OS X and/or on an iPod Touch.
iA Writer for OSX and iA Writer for iOS
Only 0.7 MB in size. (Mac version) The iOS version is iPad only.

Fullscreen
Autosave
Reading time, word and character counter
sync via Dropbox or iCloud
supports TextExpander Touch