The command indicated to get the submodules dependencies is: git submodules update --init --recursive
instead of git submodule update --init --recursive

I‘m looking for a stable paxos implementation in C++. Since the library is comprised of different modules, how would you describe the production readiness of athena? Is it used in bigger software projects, does it handle the nasty edge cases of paxos etc?

I do not know anything about the internals of the elle library, but
at echo_server.cc, line 61 there is the following code:

while (true)
    {
    // Yield until reading "<...>\n".
    elle::Buffer line = socket->read_until("\n");
    // Write the line we just get (this yields too).
    socket->write(line);
    }

Depending on the implementation and possible limits set somewhere in the
implementation of the elle library, the line

    elle::Buffer line = socket->read_until("\n");

might allow an attack, where the input stream contains about
1TB worth of characters without containing a single line break.
That might exhaust the RAM of the computer or just crash the
application, if the limits are met.
If the read_until(...) is part of the infinit, then may be in some corner case
it might also crash the infinit server.

Unable to build with fresh version of g++ compiler:

g++ -v
Using built-in specs.
COLLECT_GCC=g++
COLLECT_LTO_WRAPPER=/usr/lib/gcc/x86_64-linux-gnu/7/lto-wrapper
OFFLOAD_TARGET_NAMES=nvptx-none
OFFLOAD_TARGET_DEFAULT=1
Target: x86_64-linux-gnu
Configured with: ../src/configure -v --with-pkgversion='Ubuntu 7.3.0-11ubuntu1' --with-bugurl=file:///usr/share/doc/gcc-7/README.Bugs --enable-languages=c,ada,c++,go,brig,d,fortran,objc,obj-c++ --prefix=/usr --with-gcc-major-version-only --program-suffix=-7 --program-prefix=x86_64-linux-gnu- --enable-shared --enable-linker-build-id --libexecdir=/usr/lib --without-included-gettext --enable-threads=posix --libdir=/usr/lib --enable-nls --with-sysroot=/ --enable-clocale=gnu --enable-libstdcxx-debug --enable-libstdcxx-time=yes --with-default-libstdcxx-abi=new --enable-gnu-unique-object --disable-vtable-verify --enable-libmpx --enable-plugin --enable-default-pie --with-system-zlib --with-target-system-zlib --enable-objc-gc=auto --enable-multiarch --disable-werror --with-arch-32=i686 --with-abi=m64 --with-multilib-list=m32,m64,mx32 --enable-multilib --with-tune=generic --enable-offload-targets=nvptx-none --without-cuda-driver --enable-checking=release --build=x86_64-linux-gnu --host=x86_64-linux-gnu --target=x86_64-linux-gnu
Thread model: posix
gcc version 7.3.0 (Ubuntu 7.3.0-11ubuntu1)

errors look like:
In file included from ../../src/elle/reactor/Channel.hh:163:0,
from ../../src/elle/reactor/Generator.hh:5,
from ../../src/elle/reactor/Generator.cc:1:
../../src/elle/reactor/Channel.hxx: In member function ‘const T& elle::reactor::Channel<T, Container>::peek() const’:
../../src/elle/reactor/Channel.hxx:193:42: error: no matching function for call to ‘wait(const elle::reactor::Barrier&)’
reactor::wait(this->_read_barrier);
^
In file included from ../../src/elle/reactor/Channel.hxx:3:0,
from ../../src/elle/reactor/Channel.hh:163,
from ../../src/elle/reactor/Generator.hh:5,
from ../../src/elle/reactor/Generator.cc:1:
../../src/elle/reactor/scheduler.hh:332:5: note: candidate: bool elle::reactor::wait(elle::reactor::Waitable&, elle::DurationOpt)
wait(Waitable& waitable, DurationOpt timeout = {});
^~~~
../../src/elle/reactor/scheduler.hh:332:5: note: conversion of argument 1 would be ill-formed:
../../src/elle/reactor/scheduler.hh:335:5: note: candidate: bool elle::reactor::wait(const Waitables&, elle::DurationOpt)
wait(Waitables const& waitables, DurationOpt timeout = {});
^~~~
../../src/elle/reactor/scheduler.hh:335:5: note: no known conversion for argument 1 from ‘const elle::reactor::Barrier’ to ‘const Waitables& {aka const std::vectorelle::reactor::Waitable*&}’
../../src/elle/reactor/scheduler.hh:338:5: note: candidate: bool elle::reactor::wait(const std::vector<std::reference_wrapperelle::reactor::Waitable >&, elle::DurationOpt)
wait(std::vector<std::reference_wrapper> const& waitables,
^~~~
../../src/elle/reactor/scheduler.hh:338:5: note: no known conversion for argument 1 from ‘const elle::reactor::Barrier’ to ‘const std::vector<std::reference_wrapperelle::reactor::Waitable >&’
../../src/elle/reactor/scheduler.hh:342:5: note: candidate: void elle::reactor::wait(boost::signals2::signal<void()>&)
wait(boost::signals2::signal<void ()>& signal);
^~~~
../../src/elle/reactor/scheduler.hh:342:5: note: no known conversion for argument 1 from ‘const elle::reactor::Barrier’ to ‘boost::signals2::signal<void()>&’
In file included from ../../src/elle/reactor/scheduler.hh:379:0,
from ../../src/elle/reactor/Channel.hxx:3,
from ../../src/elle/reactor/Channel.hh:163,
from ../../src/elle/reactor/Generator.hh:5,
from ../../src/elle/reactor/Generator.cc:1:
../../src/elle/reactor/scheduler.hxx:122:5: note: candidate: template<class Prototype, class ... Args> void elle::reactor::wait(boost::signals2::signal&, Args&& ...)
wait(boost::signals2::signal& signal, Args&& ... args)
^~~~
../../src/elle/reactor/scheduler.hxx:122:5: note: template argument deduction/substitution failed:
In file included from ../../src/elle/reactor/Channel.hh:163:0,
from ../../src/elle/reactor/Generator.hh:5,
from ../../src/elle/reactor/Generator.cc:1:
../../src/elle/reactor/Channel.hxx:193:42: note: types ‘boost::signals2::signal’ and ‘const elle::reactor::Barrier’ have incompatible cv-qualifiers
reactor::wait(this->_read_barrier);
^
and lots of warnings like:
In file included from ../../src/elle/serialization.hh:4:0,
from ../../src/elle/Exception.hh:9,
from ../../src/elle/Error.hh:3,
from ../../src/elle/cryptography/Error.hh:3,
from ../../src/elle/cryptography/dsa/PrivateKey.cc:9:
../../src/elle/Version.hh:75:13: warning: In the GNU C Library, "minor" is defined
by <sys/sysmacros.h>. For historical compatibility, it is
currently defined by <sys/types.h> as well, but we plan to
remove this soon. To use "minor", include <sys/sysmacros.h>
directly. If you did not intend to use a system-defined macro
"minor", you should undefine it after including <sys/types.h>.
ELLE_ATTRIBUTE_R(uint8_t, minor);
^~~~~~~~~~~~~~~~~~~~~~~~~

An extra null pointer check is not needed in functions like the following.

• Reachability
• reactor_pthread_mutex_destroy

In the .gitmodules file, the path for the drake dependency is ../drake. Shouldn't it be the path towards your drake's fork repository on github?

Same for miniupnp, libutp and dokan.