Markdown language (ok for the non geeks text files with markup)

That renders it into HTML and a few others now has tracking changes mark up

I am doing a lot of my personal fiction in markdown, small files and almost perpetual, unlike more modern formats.

For your track changes here you go

http://m.cultofmac.com/cultofmac/#!/entry/multimarkdown-composer-gets-amazing-20-update,5112692dd7fc7b56701ac467

If you have a Mac, highly recommend markdown composer. I am using Editorial in my iOS device and of course Dropbox. Editorial, you can add the language.