I use office zilla and I think that it is the easiest for that. I have a log in on my homepage that the clients can log into for project management and they can see where their stuff is at in time wise of being completed. They can upload files there and get them when they are complete and need them. Two of my clients have started using the forum on there and they have asked me to upload articles I come across for my field as well as theirs. They can create log ins for others that may need it like a business partner or someone that will be helping them.
Just a great lil piece of software.

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Rebecca Thompson
CLR Virtual Connection * fanTABulous fan pages