The HSMP or Highly Skilled Migrant Permit scheme was, as the name suggests, for Highly Skilled Workers including contractors and freelancers to freely provide their services in the UK.
It was replaced by the Tier 1 (General) Visa. It's similar to the work permit hsmp but has some significant changes to the application form. As of April 2011 the Tier 1 (General) Visa has been closed for applicants outside the UK.
A summary of the changes to the hsmp application process are here. You can also check on the Home Office Border Agency Official Tier 1 General Visa Points Calculator to see if you qualify but bear in mind this is only for those who are already in the UK on a Tier 1. You may also want to consider switching from a Tier 1 to a Tier 2 visa.
We also have alot of information for contractors who were on HSMP and now need to extend or switch their visa to Tier 1 in our Immigration Questions and Answers.
Lastly if you're on the HSMP and worried about your renewal - check Tier 1 Highly Skilled Worker (HSMP) Visa Compliant Tax Structures for payment structures that will help you!