I am a basic Linux user and would like to backup my data (my
home directory to be precise) in an external hard drive (EHD), but would like to be able to retrieve this data in other operating systems (Linux, because I will want to retrieve my data in the future if something bad happens to my system, or Windows, if my girlfriend wants some pictures I own, or OS X, if a friend of mine wants some books I have, or *BSD, since I will have it running in another machine soon). However I am having a really hard time figuring out how to do it. What I thought would be copy/paste process is turning into a nightmare.
I've done a fair amount of research and the only thing I have understood (or think I have!) is that depending on the operating system I will be retrieving my data from, I will need to format my EHD with a different file system. In other words, if I got it right, that it is not possible to make a backup in the way I describe above. Nonetheless this is, surprisingly, a pretty undocumented process in the web. So I would like to ask: Is there a way to make a "universal backup" of my data as I described it in the first paragraph?