For me the slow start-up and the JIT requiring ~50K/req for warm-up just ruin the whole experience in coding the app in Ruby I'd rather just use Elixir.
Another interesting project is IBM's OMR [0] - compared to JRuby there are no slow start-ups and weirdly, being still a dev. preview it can run Rails and its deps. without issues, even better than Rubinius stable.
If we're very lucky, Substrate VM will be released at some point, solving the startup time issues (and I believe many of the JIT issues, though less clear on that): http://lafo.ssw.uni-linz.ac.at/papers/2013_JVMLanguageSummit...
The OMR project definitely looks interesting, but it doesn't seem to be actively developed (or perhaps the most recent commits are just not public yet). But if it works that well, then maybe there's no need, hah. Will have to try it out.
The source code is here: https://github.com/rubyomr-preview/ruby
Seems the code is being developed internally to IBM. First the docker images of the OMR tech preview were dropped about a year ago. The the source was dropped recently. Targets Ruby 2.2 so I'm going to open an issue asking about targeting 2.3 and folding this work into trunk.
$ git clone https://github.com/rubyomr-preview/ruby.git --branch ruby_2_2_omr --recursive
$ cd ruby
$ autoconf
$ ./configure SPEC=linux_x86-64 --with-omr-jit
$ make
$ make install
We haven't turned on the issue tracker on that repo, but the glue has it's issues turned on: https://github.com/rubyomr-preview/rbjitglue
Working on smoothing this out a bit, and also currently working on upgrading the JIT to target 2.4
Ruby+OMR is developed in three pieces: 1) the language independent core, then 2) The language dependent portions (i.e., the VM, and what we call the 'glue')
The language independent core is here: https://github.com/eclipse/omr. It's under active development, :)
I'm actually working on Ruby 2.4 support right now (supremely not prime time, but if you're curious, the branch is here: https://github.com/mgaudet/ruby/tree/ruby_2_4_omr_preliminar...)