Using registered servers tab in ssms

Register all sql servers under registeres servers in ssms,either by adding manually or using a regsrvr file

1) Right click local databases and import-->

2)Select the exported file which has a list of already existing servers exported from someone else's. It is in .regsrvr format.

Once all servers are registered a query can be run across all of them at one.

Very useful to see:
Exec sp_who2
Exec sp_whoisactive
server configurations etc