Padlet is quite a nice tool. You can experiment with it, I am sure your you will like it.
Here is my sample.

And hereis the padlet I prepared for you, please feel free to add your ideas there. It used to be called Wallwisher, that is why I speak about wallwisher there.
You can also create your own padlet, go to

You can also use Linoit for the same thing.
Here is my example, you can play with it, everybody can do changes in this one. However, the setting of the linoit is up to you, it can be completely private.
To create your own go to

You can also embed it in your wiki and then you can work directly from your wiki and add messages there..

Or you can upload it as a link and get to the linoit by clicking to the small picture of it.