Actually not just for US Citizens From the cbp.gov site:
Can I join Global Entry if I am not a U.S. citizen or U.S. lawful permanent resident?
Global Entry is also available to citizens of the Netherlands who are enrolled in Privium and Korean Smart Entry Service members. Citizens of Mexico may also apply for Global Entry. Canadian NEXUS members have Global Entry benefits, but are not eligible to join.
Are all U.S. visa classifications eligible for participation in Global Entry?
If your country has a bilateral trusted traveler arrangement with CBP, you may participate in Global Entry provided you are not entering the U.S. under one of the following visa categories: There is a long list of the Visa types here
There are other programs for other countries listed here