Padlet is a virtual bulletin board created online (not an app). You create it and your students post to it. Think of poster paper and sticky notes. The uses are endless. I love to use it in my classroom as an exit ticket activity--or even just to check in. I also use it in my professional development trainings. I found a great visual with lots of ideas from @simplysuzy and http://blogs.falmouth.k12.ma.us/simplysuzy/2014/02/02/padleting-together/. Give this a try, you will love it!
Click here to start: https://padlet.com