I have a co-worker who leads an industry organisation of around 300 people.  They are looking for an easy to use cloud hosted forum software.  They currently use an email based one (that I have forgotten the name of) but is entirely email based.

The main purposes would be people from different organisations asking and answering questions and seeking advice.  They are not IT people.

As the organisation relies on members contributions the cost needs to be as low as possible.

Any suggestions?