tools to ensure a clients expectations for a project are met.
validation ensures that the product actually meets the user's needs, and that the specifications were correct in the first place, while verification is ensuring that the product has been built according to the requirements and design specifications. wiki/Verification_and_validation
During analysis phases, you use different tools to ensure that you have gathered the correct requirements such as Use Case diagrams, Activity Diagrams, Class Diagrams, ERDs, Truth tables, flow charts and other business rules documents. The customer should review and approve most of these documents to ensure specification correctness.
During Design, you could use use-cases and prototyping tools/techniques to ensure the user acceptance of GUI, forms and usability aspects.
During UAT, you could use automated testing tools as well as manual testing together with use cases, test case scenarios to verify that the system fits the requirements. You could also make use of Requirements Tractability Matrix
Eventually, one could say that when functional and non-functional requirements are met the process ends (which might extend beyond the development project life time).
In addition to the above mentioned tools, Word Processors, Spreadsheets and formal requirements management tools such as DOORS may be used. If you are seeking quality measurement then some statistical tools may be require as well.
I disagree with the above mentioned reference (wiki/Verification_and_validation) at the point where the reference says, when talking about validation: "This is done through dynamic testing and other forms of review." . My understanding is that it should be "verification" instead.