NumLink Free is a great game you can play to kill time. What's great about it is that it has one simple mechanic; connect the two same colored number blocks. 

It is very easy and fun to play, however, the levels get more challenging as you clear them. But don't worry because you can use hints to help you triumph at the end.

The game has 5 models for you to enjoy with 4x4 being the easiest and 8x8 the trickiest. 

All levels are free to play and don't have any in-app purchases.

So what are you waiting for? Get it on Google Play!