Subway Idle is a casual game belonging to the sub-genre of idle clickers where players have to control the flow of trains on a metro line.
The Subway Idle mechanics are the following: you start with the first metro line of a famous city (for example, New York). At the beginning, this line has just one train and two stops. However, as you tap on the train and earn money for tickets sold, you can invest in adding more stops and trains to the line. What's more, you can invest in the speed of the trains, making them pass each stop more often in less time, as well as increase the price of the tickets.
Little by little you move up the levels, unlocking new metro lines inside the same city and investing in more trains, faster trains, more metro stations, etc. When you have completed the metro map of the city in question, you move on to another, and the investments become easier and easier, given that you will have more trains under your control giving you money automatically and non-stop.
Subway Idle is an idle clicker with a simple premise and mechanic, but it ends up being a fun, entertaining and addictive game like genres of this type usually are.