Lookup from one table to another table on different APP

Thanks for the input.  Were evaluating this as replacement to our existing CRM.  Though in the learning curve I like to find limitations and try to break things ;-)  and we currently have many related objects because of field limitations.  Another option (not sure if will work) is take this other application and just create a new table on existing APP, which brings up new question -  can you copy all of an APPS fields etc into a table or is this a "recreation