Installation with composer
The easiest way for a developer to try out MODX3 is using composer with the following command:
composer create-project modx/revolution www 3.x-dev
This will install MODX3 in a folder called 'www'. You can change this folder to whatever you want. After composer install, just go to http://your-path-to-modx.tld/setup/ to do the usual MODX installation.