Collaborize Classroom allows students to collaborize and work together on brainstorming, discussions etc.
Padlet is an electronic corkboard which is great for group work and collaboration. Students are able to add their comments, links, pictures or videos and this set of training videos outlines Padlet and in oarticular the controls that you the teracher has.
Bubbl.us is a very simple interactive mind mapping tool and these videos outline the different tools which make it such a good tool for students to use.
If you are working with groups of students and you want them to brainstorm on ideas or collaborate with students then you might want to consider this tool. The interface is great and so easy to use.
Today's Meet allows you to have live feeds in lectures, conferences and lessons and is so easy to use. These videos detail the different settings on Today's Meet and outline features such as restricting access to rooms and QR codes.
In Tricider you can write a question, generate a weblink and then share the weblink with your students and they can click on the link and add their answers. The format is really nice and it means you can also add a question, write a series of suggested answers and get the students to comment on them.