Lumosity: https://www.lumosity.com/en/ - A well-known website offering brain training games designed to improve memory, attention, flexibility, problem-solving, and speed. Lumosity offers a free trial and paid subscription plans.
Elevate: https://elevateapp.com/ - Another popular brain training platform with games targeting memory, processing speed, focus, critical thinking, and proficiency. Elevate provides a free limited version and paid subscriptions for full access.