Postgres architecture for one machine with several apps

I have one machine on which several applications are hosted. Applications work on separated data and don't interact - each application only needs access to its own data. I want to use PostgreSQL as RDBMS. Which one of the following is best and why?

1. One global Postgres sever, one global database, one schema per application.
2. One global Postgres server, one database per application.
3. One Postgres server per application.

Feel free to suggest additional architectures if you think they would be better than the ones above.