In the current article, we will see what is actually the difference between the CRM plugin and the redmine_crm gem.
The CRM plugin and Contacts plugin are the same thing. It is the plugin itself and could be checked here.
The redmine_crm gem is actually installed in the 3-rd step of the installation guide. So, it is just a gem that is required for the plugin to be able to run. More information about the gem itself could be seen here.
Note: Please note that the redmine_crm gem is part not only of the Contacts plugin but also some other plugins that do not require the Contacts plugin to be able to work, for example Agile and People plugins. In other words, you could install Agile and People plugins without the Contacts plugin. The redmine_crm gem will be simply installed during the installation steps.