How can I merge two tables?

Hi,

I have tables on my various computers that looks like:

            Table "public.registrations"
 Column  | Type | Modifiers | Storage  | Description
----------+------+-----------+----------+-------------
software | text |           | extended |
id       | text |           | extended |
value    | text |           | extended |
location | text |           | extended |
Indexes:
   "registrations_software_idx" btree (software) CLUSTER
Has OIDs: yes

I keep registration numbers for software and login/passwords for
various organizations, etc…

As time goes by the tables on the various computers get out of
sync.

Is there an elegant way I can get all of the differences (uniquely)
merged into a single table?

Thanks

Jerry