Simple Notes, Simple Calendar, Simple Clock .... looks like at least 18 apps. On Google Play Store
They recently added an 'Accelerate language Learning' session to the 'Peak Performance' collection which used to be for exercise/sports/phys ed stuff only. Designed for Human natural languages I think but may work well for sign and programming languages and creoles/pidgins too.
When Apple bought Dark Sky, they made it an Apple only app. Some person created Dark Sky as a work-alike for all us in Android world. Don't know if he(i think?) works entirely by himself with open source foundations or contracts out to freelancers. Answers emails.