How many databases can I create on a single Amazon RDS instance

http://aws.amazon.com/rds/faqs/#2

Multiple MySQL databases or SQL Server databases (up to 30) or Oracle database schemas can be created on a given DB Instance.

Update 2013-12-16: as discussed in the comments below, the wording in the RDS FAQ is ambiguous. @Jan sent an inquiry to Amazon, and got this reply:

With RDS MySQL database instances, it follows the MySQL standard where there's no limit on the number of databases - http://dev.mysql.com/doc/refman/5.5/en/database-count-limit.html. Thank you for pointing out the spotty documentation there, we'll amend that to make it more clear.

Thanks @Jan!

Update 2014-08-26: the RDS FAQ now states:

• RDS for MySQL: No limit imposed by software
• RDS for Oracle: 1 database per instance; no limit on number of schemas per database imposed by software
• RDS for SQL Server: 30 databases per instance
• RDS for PostgreSQL: No limit imposed by software

And that makes one wonder, "how many instances can I have?"

By default, customers are allowed to have up to a total of 40 Amazon RDS DB instances. Of those 40, up to 10 can be Oracle or SQL Server DB Instances under the "License Included" model. All 40 can be used for MySQL, Oracle, SQL Server, or PostgreSQL under the "BYOL" model. If your application requires more DB Instances, you can request additional DB Instances via this request form.

As per the AWS document -

• RDS for Amazon Aurora: No limit imposed by software
• RDS for MySQL: No limit imposed by software
• RDS for MariaDB: No limit imposed by software
• RDS for Oracle: 1 database per instance; no limit on number ofschemas per database imposed by software
• RDS for SQL Server: Up to 100 databases per instance(The maximum number of databases supported on a DB instance depends on the instance class type and the availability mode—Single-AZ, Multi-AZ Database Mirroring, or Multi-AZ Availability Groups. The Microsoft SQL Server system databases don't count toward this limit.) see here: AmazonRDS SQL Server User Guide
• RDS for PostgreSQL: No limit imposed by software