The document discusses several lean startup tools for validating problems and solutions, including: - Problem/Solution Canvas for outlining customers' problems, your solution, and assumptions to test. - Business Model Canvas for visualizing key aspects of a business like customer segments and revenue streams. - Launchrock, Unbounce, and Kissmetrics for testing if people are interested and will take desired actions like signing up. - Snapengage for talking to interested customers live on a site to better understand engagement. - Usertesting.com for getting people to test products and provide feedback.