Mathletics - Students in Years 1 to 6 have access to Mathletics
https://www.mathletics.com/au/
ABC Splash Mathematics - for K-10. ABC Splash has resources across all KLAs. This links to their mathematics resources which can be searched by key word and filtered by grade.
https://education.abc.net.au/home#!/resources/-/mathematics
ReSolve -Maths by Inquiry for K-10. It is a collaboration of the Australian Academy of Science and the Australian Association of Mathematics Teachers. The tasks and materials on reSolve promote fluency, deep understanding, strategic problem solving, and mathematical reasoning through enquiry. https://www.resolve.edu.au/teaching-resources
NRICH - for K-12. NRICH provide thousands of free online mathematics resources for ages 3 to 18, covering all stages of early years, primary and secondary school education with a focus on developing mathematical thinking and problem-solving skills (University of Cambridge). https://nrich.maths.org/
Youcubed - for K-12. Jo Boaler and her team at Stanford University provide research-based teaching methods, maths tasks, videos, and ideas for extending thinking and inspiring teachers and students. https://www.youcubed.org/tasks/
GeoGebra - for K-12 is dynamic mathematics software for all levels of education. There are free activities, simulations, exercises, lessons, and games for math and science. https://www.geogebra.org/
MoneySmart - Free, engaging, curriculum-aligned classroom resources. https://moneysmart.gov.au/teaching-resources
Red dragonfly mathematics challenge - for Years 5 and 6. Provides a range of challenges to be solved in five to ten minutes that develop mathematical reasoning. https://schoolsequella.det.nsw.edu.au/file/20a29ac1-c6f3-4ca3-84b1-2d8488a4cbcd/1/reddragonfly.zip/index.html