Q:

How do I install Neovim with GUI and msgpack support in Ubuntu?

I would like to get Neovim because of its msgpack API and clear roadmap of development, but it is not in Ubuntu 16.04's repositories.
 Command 'gvim' from package 'vim' (main)
 Command 'gvim' from package 'vim-gtk3' (universe)
 Command 'gvim' from package 'vim-gnome' (main)
 Command 'gvim' from package 'vim-athena' (universe)
 Command 'gvim' from package 'vim-nox-py2' (universe)
 Command 'gvim' from package 'vim-gtk-py2' (universe)
 Command 'gvim' from package 'vim-nox' (universe)
 Command 'gvim' from package 'vim-gtk3-py2' (universe)
 Command 'gvim' from package 'vim-gnome-py2' (universe)
 Command 'gvim' from package 'vim-tiny' (main)
 Command 'gvim' from package 'vim-gtk' (universe)
 Command 'gvim' from package 'vim-athena-py2' (universe)

I have now selected vim-gtk3 but it may limit me later.

How do I get graphical Neovim with msgpack support?

A:

Instructions can be found on the Neovim Wiki
As of the posting of this answer, the site's current instructions are as follows:
Ubuntu
Neovim has been added to a Personal Package Archive which allows you to install it using apt-get on Ubuntu 12.04 and later.
To be able to use add-apt-repository you may need to install software-properties-common:
sudo apt-get install software-properties-common

If you're using an older version Ubuntu you have to use:
sudo apt-get install python-software-properties

Run the following commands:
sudo add-apt-repository ppa:neovim-ppa/unstable
sudo apt-get update
sudo apt-get install neovim

Prerequisites for the Python modules:
sudo apt-get install python-dev python-pip python3-dev python3-pip

If you're using an older version Ubuntu you have to use:
sudo apt-get install python-dev python-pip python3-dev
sudo apt-get install python3-setuptools
sudo easy_install3 pip

For instructions on how to install the Python modules, see :help nvim_python.
If you want to use Neovim for some (or all) of the editor alternatives, use the following commands:
sudo update-alternatives --install /usr/bin/vi vi /usr/bin/nvim 60
sudo update-alternatives --config vi
sudo update-alternatives --install /usr/bin/vim vim /usr/bin/nvim 60
sudo update-alternatives --config vim
sudo update-alternatives --install /usr/bin/editor editor /usr/bin/nvim 60
sudo update-alternatives --config editor

Note, however, that special interfaces, like view for nvim -R, are not supported.  (See #1646 and #2008.)

The GUI portion needs to be installed separately. See the list of 3rd party GUIs on the Neovim site. 

