Multi-project can be installed from the Melpa package repository for Emacs by adding an entry for Melpa. The link below describes how to install Melpa.
Invoking M-x list-packages will list all of the available packages from the Melpa repository. Typing 'i' at the listing for Multi-project and then 'x' will install it.
The other way to install Multi-project is to download the multi-project.el file and add it to the emacs load-path and then add the following lines within your .emacs file:
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