What government restrictions are imposed on the business activities of foreigners in Thailand?
The Foreign Business Act 1999  regulates the business activities of foreigners in Thailand. The act classifies business activity into three categories and places restrictions of various degrees of severity on foreign ownership and operation of these businesses.

Can foreigners hold 100% ownership of a business in Thailand?
Foreigners can hold 100% ownership of businesses in non-restricted categories, such as exporting businesses and certain types of manufacturing businesses. Other methods to obtain 100% non-Thai control are through (1) application for an alien business license (2) Board of Investment (BOI) Promotion which may include assistance with an alien business license (3) registration through the Treaty of Amity (if you are an American).  Read more about Foreign Companies.

Are there other alternatives to a foreign majority company?
The vast majority of foreigners in Thailand register a Thai majority company.  This is a company that has 51% or more of Thai shareholders.  Rtead more about Thai Companies.