I think the Wallwisher is an excellent and easy way to can post announcements and questions. Students don't have to create an account. I can post questions related to any subject area and students can respond to them during centers time. I will be the only one to read their responses, and at the same time, check for understanding.
I also created a Skype account. This program will allow me and my students to connect with other classes from the district and around the world without leaving the classroom. I like the idea of inviting guest speakers, share information with other teachers/classes through this program in the classroom.