ACOUCOU is an interactive, online training platform for acoustics. It offers a set of free educational materials in various fields of acoustics, available under the CC BY-NC-ND 4.0 license (Creative Commons license).
Acoustics Knowledge Alliance (ASKNOW) includes five free, interactive courses on the platform:

Fundamentals of Acoustics;
Psychoacoustics;
Acoustic Simulations and Auralization;
Electroacoustics;
and Architectural Acoustics.

Each of these five courses consists of 30 lessons and 2 case studies. Each lesson consists of three parts: a theoretical part (Part A), an interactive part (Part B) and a part of assignments (Part C).
Courses: https://asknow.acoucou.org/
Promotional video (room & building course): https://www.youtube.com/watch?v=kORXF_xwvz0 ACOUCOU for Architecture
ACOUCOU for Architecture The Architecture module contains visual materials to help architects and designers familiarize themselves with architectural acoustics.

Case studies: https://acoucou.org/architectureArAc
Multibook: https://arac-multibook.com/
Promotional video: https://www.youtube.com/watch?v=Xz7-_rWNcHE