My favorite one is LightPaper (http://www.ashokgelal.com/lightpaper-for-mac/ http://www.ashokgelal.com/lightpaper-for-mac/). With multitabs and a folder navigat

My favorite one is LightPaper (http://www.ashokgelal.com/lightpaper-for-mac/ http://www.ashokgelal.com/lightpaper-for-mac/). With multitabs and a folder navigator, among others, I can keep and edit related documents together. I wish it had a vi mode but other than that it's perfect.