I am personally working on a tiny side project to build a chat/forum/etc platform based around onion services for all users. Traditionally, it was annoying to have to ask users to install Tor and open up the control port so your app could leverage it. In a recent alpha there is an experimental tiny little C API that can start the Tor system in-app [0]. Leveraging some of the work from [1], I put in some effort to get all the steps working to compile Tor statically in a a single Rust exe on Windows [2]. As Tor's embeddability game increases, I hope more apps will consider using it as part of their network stack. Granted I know the problems that are inherent with "vendoring" security libs like these, but for some uses the benefits outweigh the costs of requiring separate downloads and separate daemons running.
0 - https://blog.torproject.org/tor-0331-alpha-released-back-uns... 1 - https://github.com/iCepa/Tor.framework 2 - https://github.com/cretz/rtsw-poc