enabling offline/mainly offline usage
That's self-inconsistent. You can't use what's offline. If it's usile, it's online. Enabling use of it entails making it online.
The closest existing thing is probably E-Mail
This is instructive. eMail is a great decentralized peer-to-peer application, with some major flaws. Some are trying to compete with this great, flawed, popular system.
The Internet is completely decentralized.
No, it's not. And there's no such thing. Nothing is completely decentralized, except grey goo vel cetera. An internet, fundamentally, is a noncentralizate. Nonetheless, a centralizate can comprise noncentralizates.
I don't know the proper name. Decentralized web applications? Peer-to-Peer applications?
How about calling it ``you have your stuff, I have my stuff; let's have our stuff interact, without any 3^{rd}-party'' as an extension of the ``what happens among some mutually consenting persons that doesn't affect anyone else, is the concern of only those mutually consenting persons, unless those mutually consenting persons make it someone else's concern'' principle---using general personhood, naturally.
It seems that you're lacking some fundamental understanding. The 1^{st} question you should ask is whether you understand each fundamental informatical, relevant mathematical. (You might read Knuth's The Art Of Computer Programming.) If you understand these, then it should be easy to learn about a particular informatical, starting with special informaticals, germane mathematicals. (The 0^{th} question you should ask is whether you understand solipsism.)
I can't write about all these protocols if I haven't studied them thoroughly. And for that I need to read this document first, or any similar centralized synthetic resource.
No. It's sufficient to read such a document first. Probably, it's not necessary, but better, to understand about what you write.
What would Knuth do?
study each [related] software thoroughly ... comparing them
synthetizing a high-level overview
Each serious project should be such that any general intelligence can easily work with it.
Write the document first, and then think about where to publish it.
And when you write the document, consider each way you can publish it, to write it so that it's easy to translate to a form that's easy to publish in many (try: each) those ways.