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