Academy of Inquiry-Based Learning - AIBL has many resources on their website for instructors using IBL. They also organize the IBL Workshops each summer.
Journal of Inquiry Based Learning in Mathematics (JIBLM) - Free and peer-reviewed IBL textbooks/question sequences for many courses in mathematics.
Discovering the Art of Mathematics - More free inquiry-based course materials.
Active Calculus - A free, open source, inquiry-based textbook for Calculus by Matt Boelkins, David Austin, and Steven Schlicker of Grand Valley State University. Both single variable and multivariable editions are available.
TPSEMATH ACTIVE LEARNING RESOURCES- TPS Math provides resources for educators, students, and institutions of all sizes, including support for internships, all focused on enhancing math education.
Team-Based Inquiry Learning- TBIL is an implementation of Team-Based Learning as Inquiry-Based Learning for mathematics.
Inquiry-Oriented Differential Equations- Inquiry-Oriented Differential Equations (IODE) is a first course in differential equations focused on understanding of the big ideas in first order, second order, nonlinear, and systems of differential equations.
Inquiry-Oriented Linear Algebra- The IOLA project focuses on developing challenging tasks and instructional materials to foster an inquiry-based approach to teaching and learning linear algebra.