One is an a la carte program of college level classes that's the traditional method for earning higher education credits for precocious high school students. The other is a two-year, well-rounded syllabus created in Switzerland and (at different points in its 40-plus year run) financed by UNESCO and the Gates Foundation, which is gaining steam. They are the Advanced Placement and International Baccalaureate programs, respectively.
According to a recent blog post over at The Washington Post, schools, such as Colorado College, are allowing scores from either of their tests to replace the SAT and ACT in college admissions. But, because of its expense and affiliation with the United Nations and liberal ideologies, the IB faces some opposition.