We need to implement CMMI. What is the best tool to do this?
Excuse me while I take a tool to my head. . . oh, sorry, I thought I was in the wood shop!
By far the best tool to use for CMMI is the one between your ears.
Applying logic and sound business judgment in selecting your approach, who should be involved, and how success is defined will be the single most important “tool” in your arsenal.
I worked with a client once who spent millions on a “tool” to “do CMMI” but they gave a blank stare when asked about their business goals and objectives.
That said, you'll likely end up with more than one new toy to play with if you decide to go agead and buy something.