I have used Socrative, Lets Geddit, Kahoot, etc. and really enjoy them, each seemed to accomplish the task of quick online formative assessments well and each had it's pros and cons. Overall, I felt like my toolbox in this arena was already full. When I went to MACUL 2015, I really wasn't looking for another online formative assessment tool.
HOWEVER, I was at the SIGEE meeting at MACUL and my friend John (@bcgeek) introduced me to Formative (https://goformative.com/). WOW! After a month delay, I finally got a chance to check it out and I am impressed. The user interface is clean and easy to use. You can upload PDF, Word files, or Google Docs and easily convert them to an online assessment. You can see students answering the assessment in real time. The list goes on and on! Try it out in your classrooms and let me know what you think!
To get started, here is a quick introductory video: