For underrepresented or underserved students:
The Math Alliance is a great resource for all underrepresented or underserved students in math: https://mathalliance.org/welcome/
The Tapia Center at Rice University does great work to support underrepresented STEM students. You might be interested in their graduate program: https://tapiacenter.rice.edu/
The Conference for African American Researchers in the Mathematical Sciences (CAARMS)is held annually, and usually has tutorials for undergraduates, poster sessions, and talks by African American researchers in math.
For women in math:
This link contains a bunch of resources for you: https://sites.google.com/site/awmmath/info/undergrads
The postbac program at Smith may be of interest to women undergrads: https://www.smith.edu/academics/mathematics-statistics#center