Depending on what you would like to do, there are two potential approaches.
On the simple end, you have fields on content types that only certain roles can edit. For example, you can have a field called vetted and two roles, author and expert. When an author makes a new node, vetted would get set to some default value, like not verified. Your expert users can then read and review the nodes, and sets the vetted field as appropriate, say verified or needs further review.
One the more complex end, you can use workflow. Two modules that do this are Workflow and Workbench. With this, you can set up just about any editorial review process that you want. Both can also be combined with Drupal actions to occur on state transitions. Just keep in mind that workflow can be a pain to set up, and often there are real work scenarios that don't always work into rigid workflow rules.
As for existing systems, Open Atrium may potentially fit the bill. It is more designed for team collaboration, but based on what clients have said, it may work for something more conference oriented.