Mac – Something like Dropbox for local use with a NAS as storage server

You and Zlatev are on the right track with Offline Files. Your NAS has to run Windows. Under the Group Policies, you'll want to configure "Slow Link Mode." Just jack the setting up to like 999999 Kbps. This essentially forces all reads and writes to the local cache. Under Slow Link, windows will only sync about once every two minutes. Also you should probably turn off the balloon reminders. They popup initially to tell you, "Hey, you are offline! We are reading and writing stuff from local cache now!!!" Durrrrrr.

On the client side, you want to turn on "automatically cache files." It automatically caches every network file you access through that UNC path, up to 25% of your disk space. That can be adjusted too.

If you have multiple folders to share and your server is using either Linux or Vista/7, then just create a dummy share folder and hardlink all the folders you want to share to that one.

Lastly, I highly recommend that you at least upgrade the client to Vista. One of Vista's improvements was differential block writes. Only the changed parts of a file are sent back to the server. Also, the Vista/7 offline files (technically called Client Side Caching) is vastly more reliable. On the server side, all it has to do is update to the latest changes in the SMB protocol. In fact, all it has to do is use SMB. So all this is possible using any network share, as long as the server end supports SMB.

Here are some technet articles.

http://technet.microsoft.com/en-us/library/bb457104.aspx

http://technet.microsoft.com/en-us/magazine/2007.11.offline.aspx

Try the following:

rsync -av src:/dir/to/files/* /dest/dir

If you have multiple nested subdirectories, you'll need to do something like this first:

find /dir/to/files -type d -print

Run that list of directories through a loop and call rsync each time. Of course, assuming you're doing this on a remote machine, you'll need to issue the find via ssh and store the results in an array and then execute the rsync loop.