I recently installed PgAdmin 1.18.1
on my computer, with a pretty standard installation.
When I open it, I see a list of three servers, and when I create a database in one, it creates a database in all the others.
Why is this happening? What's the deal with all these servers?
The important thing is that they are 3 different connections to the same server, that's why when you make a change in one of them it propagates to the other ones.
Each one of those "servers" actually represents a connection to a database. You will add extra "server" for each different user connecting to the same database for example.
The last one, x86 probably uses a 64bit library while the second one uses a 32bit library (Because you have a 64bit OS, the second one works for backwards compatibility). The first one appears to work with a different background behaviour, as a way to offer a special Postgres feature, spatial database management (http://postgis.net/). It probably offers extra options when creating tables/columns