Fleet is a C99 library OS for unikernel applications, targeting a virtualized 32-bit i386 PC. It is a single-threaded architecture, based on asynchronous, non-blocking IO.
You will need gcc and build tools, configured for i386 or x86-64.
apt-get build-essential
If you are using an x86-64 machine, you will need i386 libc.
apt-get g++-multilib libc6-dev-i386
You will need qemu, since that provides the execution environment.
apt-get qemu
Setting up a GNU-style cross-compiler toolchain is a hassle, so I didn't. Instead, there's a Make recipe which configures CFLAGS, LDFLAGS, and LDLIBS to build a freestanding binary which uses libfleet as its system environment. There's an example in demo/Makefile, but essentially you just need to add something like this to your Makefile:
include ~/fleet/build/link.mk