I needed a popup to show only once in each browsing session of my visitors.
This option is inbuilt in only two free plugins that I found..........
1. Simple popup manager and
2. Popup scheduler
However, the popup scheduler doesn't work if you have a caching plugin installed.
Therefore 'Simple popup manager' is not only a good choice, it is the only choice.
The very best that you can get out there.
I wish they also plan to install something so that the popup comes up in each session of my visitor when he/she goes to the second page only.