SQL Server Multiple Instances License

Since SQL Server Express is free to use, If I install two instances of the same versi开发者_运维问答on on a single CPU machine, will there be any licensing issue even though it is free?

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None.

I currently have a VM that has:

• SQL Server 2005 Express
• SQL Server 2008 Express
• MySQL 5.1.49 Community
• Oracle Express (10g)

I don't recommend having them all run on start up, unless you actually need to access them.