Rich Tasks

Even more here 

https://www.nctm.org/pows/

https://www.serpinstitute.org/poster-problems/

http://map.mathshell.org/

https://access.serpinstitute.org/poster-problems/

https://artofproblemsolving.com/wiki/index.php?title=AMC_8_Problems_and_Solutions

https://nrich.maths.org/6299

https://www.youcubed.org/tasks/

https://docs.google.com/spreadsheets/d/1jXSt_CoDzyDFeJimZxnhgwOVsWkTQEsfqouLWNNC6Z4/pub?output=html

http://completemath.onmason.com/family-of-problems/

https://robertkaplinsky.com/

http://www.aimsedu.org/

http://www.insidemathematics.org/

http://www.openmiddle.com/