iPhoto Library Manager
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Full user review
"Excellent software for switching iphoto libraries."
ILM lets you create, delete and manage your iphoto libraries. It also has other useful functions like merge and rebuild. Invaluable software.
It is stupid that Apple won't let you do this within their software. But they don't, so....
If you take lots of pictures, you really need this software. Having multiple libraires lets you clean up your photo collections and quickly move between them. This is a good value and the developer is very much on top of keeping it up to date. Highly recommended.