I really like Wiktenauer. It has lots of information and translations of historical fencing treatises. As an open source format it’s great. There are some limitations though, you have to have internet and something close to a desktop environment to use it; sometimes translations are linked to external websites instead of hosted locally (often the links break); and it doesn’t include interpretations, just images, transcriptions, and translations.
I like to read treatises anytime and anywhere, and I don’t like doing word processing or printing if I don’t have to. Many books are available as open or creative commons pdfs: unfortunately they are often difficult to find. I have many pdfs that I can’t find on the internet any longer. I am going to upload these works to this post as pdfs and also as epubs for those who like to use e-readers as I do.
Please respect the rights of the original translators and don’t use these works for commercial purposes.