AFAIK there is no module or app available in the appstore with the same features, but you could model it yourself in Mendix. Basically you want to create messages in your application and share them with a form. A good starting point is to copy the features of the project wall in sprintr:
You mentioned that you tried some features, without success. The community could help you when you share the difficulties and specific problems which are occurred during development of your features.
As Samet mentioned, though there is no out-of-the-box solution in the form of a widget or module, you should be able to create your own.
Just to start it off, the way I see it, you should try to think of a message board. What do you need in order to achieve what you want? First of all, I'd say a topic entity to link your messages and a message entity which stores the messages. Start with that and try to add more functionality as you see it take shape.
Once you are able to create topics, you could simply show these with a datagrid/templategrid, so the messages are viewable by everyone.
(Ofcourse instead of Topics and Messages you could also work with Messages and Comments in a similar fashion)
Something like the news feed in the app platform, like this:
Is that possible? As an admin, i want to share newsmessages with my employees!
Anyone that can answer my comment in the initial post? :)