The ACT! Company is probably one of the worst implemented concept of ACT! Instead of a clearly defined relationship between a Contact and an Account/Company, ACT! allows the user to enter text and/or relate the record to a Company using the same field - Company Name in the Contact record. If text is entered, the Contact isn't "technically" related to the Company. To increase the confusion, the Contact can be also assigned to a Company by using dynamic Rules or manually assigning on the Company tab. Contacts can also be assigned to multiple Companies without any hint as to which one is the primary Company. The end result -- a very, very messy Contact/Company relationship.
In most CRM software, Contacts MUST be associated with an Account. Since ACT! doesn't require this, the Exporter software attempts to collect unassigned Contacts, create an Account and assign the Contacts to the Account. The created Accounts.csv is different than original Company.csv file which also extracted. Unless, there are compelling reasons to use the Company.csv data, it is recommended that it be used for reference only and ignored for the migration.
Unfortunately, the Exporter software can't interpret the "intentions" of the user. It has to follow some simple rules when building Accounts. These are listed below.
Most CRMs do not allow Contacts to be assigned to multiple Accounts. ACT! does. If this feature has been used, the Exporter software creates a column in the Contact.csv export file named X_Other_Companies. This field will contain a list of all the Companies that the Contact was assigned to. How it is dealt with in the new CRM will depend on the features available.