Our smartphone gives a lot of advantages in our lives and it has levelled the playing field on how we learn and do our daily tasks. Almost everything can be found and solved at the end of our fingertips.
Here are some apps that I have regularly used:
For class interaction: Padlet, Kahoot, Classroom
In teaching maths: Geogebra, Mathpapa, Desmoz, Mathphoto, Unit circle, Math step by step
To edit documents: Camscanner, Xodo, Speechnotes
Looking for flights, cinema, hotel, etc: Airasia, Maybank, Cimb, Tgv, Grab, Agoda
First, look at your needs and do your own research.