Need a keyword generation software created. Creates massive list of keywords.

I need a desktop OR web-based program created that will be able to scrape various websites such as Google, Amazon, Bing, etc. and pull keyword phrases. The purpose of the tool is to generate a massive list of keywords. There won't be any accompanying data with the keywords. I only need the keywords. I have detailed specs. If it's web based, the IP address used will need to be the user's IP address and not the one residing on the server. The reason being is that this will be sold, and I can't have 100s of users using a web based tool, all hitting these sites from the same IP address, as that would obviously get our server blocked. The tool needs to be multi-threaded and blazing fast (without getting IP blocked). Please reply if you've created somewhat similar programs in the past. If I choose you and you do a good job, it's very likely I'll have much more work for you. Thank you.