By default, the Alfresco installer configures Share to use an embedded Activiti engine.
To access a standalone instance of Activiti it is necessary to install the Activiti Share connector.
When this connector is installed and a user clicks on the action to start a workflow, only the workflows in the standalone instance are selectable. In the same time, Share generates links to open workflows instances associated with documents on the standalone instance and not in the embedded instance.
Is there a way to use, at the same time, the embedded Activiti and the external one?
Unfortunately, the Share connector has been build in an annoyingly naive (or deliberately aggressive) way that replaces/supercedes the standard UI pages. The Share connector should provide links in the UI to switch to the standard pages though, which would give you access to the embedded Activiti engine - at least when I last checked it out in summer of last year.