Recruitment Testing Software: Features & Requirement

I have been trying to find a good software for meeting our recruitment needs. I need a software which will allow our candidates to take a timed test online and it will score them immediately and inform us about the results. More specifically features I am looking for are:

1. Ability to conduct timed online tests
2. Ability to evaluate answers and calculate scores
3. Ability to email total score, errors etc.
4. Ability to randomize questions and answers.
5. Ability to conduct profile information validation.
6. Ability to prevent users from taking the test repeatedly.
7. Ability to compensate for browser-server round-trip time. We don’t want to penalize the test taker for slowness of browser or machine or internet connectivity.
8. Ability to revise previous answers.
9. Ability to score text answers.
10. Ability to support penalty scoring
11. Ability to automatically send different emails based upon score
12. Tamper proof. You shouldn’t be able to manipulate the time or questions in any way.

In my extensive search I couldn’t come across a single piece of software which meets these basic requirements, so I decided to write one for our recruitment tests. Do you know of any software with these capabilities. Secondly what features do you think would complement well this minimal feature set?

BTW: I have decided to use PHP as my development platform and MySQL as the database. Feel free to ask why.