Right from the home page, Colaab claims the value of its browser-based system for design revew. It uses an enhancement of Microsoft’s Silverlight technology, Deepzoom (good primer here), to allow large image files to be downloaded and viewed almost instantly. Colaab also allows on-screen annotation and mark-up, but the range of supported file formats doesn’t extend to CAD files such as DWF (extensively used in many construction collaboration platforms), so designs would have to be saved in other formats (eg: PDF, JPG) if users intended collaborating on them.
Ignoring the free single user option, Colaab prices start from $24/month up to $99/month. The latter package allows 25GB of storage, unlimited workspaces and users, and includes conference calling capabilities.