I've tried lots of docs tools, but the one I've found works best for me is a self-hosted Dokuwiki. Dokuwiki stores it's output in text files (not in a database

I've tried lots of docs tools, but the one I've found works best for me is a self-hosted Dokuwiki. Dokuwiki stores it's output in text files (not in a database) so installation is as simple as unzipping an archive, and a cron job to copy the docs directory to s3 weekly takes care of backups. As a plus, you can easily allow collaboration since it is a wiki after all. Needless to say, you can use it on any platform with a Web browser. Lack of support for markdown is the only shortcoming, but the wiki syntax is easy enough to learn.