There is the Boston area consortium consisting of 20 schools: Amherst College, Babson College, Bentley University, Berklee College of Music, Boston College, Boston University, Brandeis University, Brown University, College of the Holy Cross, Emerson College, Harvard University, Lasell University, Massachusetts Institute of Technology, Northeastern University, Olin College, Rhode Island School of Design, Suffolk University, Tufts University, Wellesley College, and Wheaton College.
https://www.boston-consortium.org/about/
Some schools in the consortium have a closer relationship than others and consortium perks vary from school to school. You can check individual school websites for more info.
For instance, at BU you can cross register at Boston College, Brandeis University, Tufts University, and also at Hebrew College [outside of the consortium].
https://www.bu.edu/reg/registration/consortia/
If you are studying philosophy at Brandeis, for example, you can cross register at Babson College, Bentley University, Olin College of Engineering and Wellesley College, as well as the undergraduate school of arts and sciences at Boston College, Boston University and Tufts University.
https://www.brandeis.edu/philosophy/courses/consortium.html
Also in the Boston area — there is a Marine Studies Consortium that allows cross-registration (14 member institutions).