You can write about anything yo uwant with an ebook. Typically they're in pdf file and may or may not include security features. There are programs yo ucan buy or subscribe to that will include more security features to prevent piracy, but if someone is determined to make a ton of copies of your book or pass it out to all of his friends it seems no matter what they'll get around whatever you've tried to include. And for the honest folks, too much security stuff can really make it hard to enjoy your ebook.
I have a few ebooks... My main one, The Cloth Diapering Handbook I just put into ebook form to see how it does. I also have a free homebirth book for children in an ebook format available for downloading and a free -book directory on cloth diapering businesses. I think I might offer the rest of my publicatons as an ebook also because I know people like the discount and the lack of waiting on the mailman (and i like not having to package books and deal with the possiblity of lost packages and damaged packages!).
You could write a book in whatever program you have for word processing and download a free pdf converter to convert that file to a pdf. This prevents the formatting from going blah on another persons computer and helps keep your project intact without people screwing around with the original document. I have actual adobe program but before it, I made all of my books in Word.
You can also download programs that you use to write your ebooks, but I was never happy with the end result (didn't seem professional to me).
Anyway like I said, you can write ebooks on whatever you want. I stick to natural family living topics but you can do whatever floats your boat!