Orchid
Orchid is a decentralized marketplace "for bandwidth"; providers run a server (in the srv-shared folder) that talks to a decentralized directory that runs on Ethereum (in the dir-ethereum folder). On top of this marketplace, we happen to provide a VPN application (the app- and vpn- folders) as well as a lower-level client daemon (currently in cli-shared); but, as our software is (and has always been ;P) entirely open-source (under a "free software" license: the AGPLv3)--and, because we strive to use "off the shelf" transport protocols whenever possible (such as WebRTC and, maybe-weirdly, layered UDP)--you can remix our stack into anything you want! Users pay for service using "(streaming) probablistic nanopayments"--a "layer 2" Ethereum scaling solution we think of as somewhere between "one-to-many payment channels" and "probablistic roll-ups", based on some older (yet seminal) work into which we poured effort into economic incentive design and practical integration--that is "somewhat separate", in case you'd want to use it for something else (you can find the code for this in lot-ethereum).
Building
To hack on any Orchid sub-project, you need to have the usual (complete) set of GNU build tools installed (such as autotools, bison/flex, make... you know, "the works" ;P) and (specifically) clang (I'm truly sorry... maybe one day we'll support gcc). Some of the build scripts for our dependencies use Python (I think only 3.x), one insists on being built using meson/ninja, and we use a couple libraries that are written in Rust. FWIW, the "usual algorithm" of "try to build it, and if you get an error saying you are missing X, just install X" should work, so I'd just dive in (like, I'm surprised you are even reading the README, am I right or am I right? ;P); that said, if you are "feeling lucky", you can run env/setup-mac.sh or env/setup-lnx.sh (two scripts we provide... you should just read them first) to install most of what you'd want. Don't forget to do a "git submodule update --init --recursive", and then you should be able to build a client or server for whatever platform you want by just going into the appropriate folder (such as app-{android,ios}, or {cli,srv}-shared) and running "make".
Alternatively, if your goal is merely to "build a copy of" Orchid--as a user who simply doesn't want to have to trust any of Orchid, Apple/Google, or GitHub to give you "safe" binaries (but feel comfortable with the source code you were provided... how you might hope to do that part is definitely left up as an exercise to the reader ;P)--you can avoid almost all of the dependencies by installing Docker and then running "env/docker.sh" instead of "make"; this will throw together a temporary development environment (by installing clang, Rust, the Android NDK, etc.) and then run make inside of the container. You do still need to have checked out the full source code (including the submodules!). (Of course, this now requires you to trust a bunch of binaries from Docker--to be clear: if you look at env/docker.sh, you can see that it is starting with a bare Ubuntu image, so at least none of these binaries come from us--which may or may not help with your particular trust scenario, but this is kind of a "last resort" to allow non-developers to "build from source", so hopefully it is useful to consider.)