Which platform/programming language to chose for a server application that synchronizes with air clients

This is my setup:

Around 60 pc's running an air client application, connected to (w)lan
1 pc that acts as a server, also connected to (w)lan

Scenario:
Whenever a change is made on the server (database and/or file change) this change needs to be synced to all air clients. (The server contacts all connected air clients one by one, to initiate the sync process)

Which platform?
The server application should be cross platform and easily installable, so my client can install the server app without any guidance (using install wizard preferably).

What comes to my mind is using a Java application for the server because I don't think an air application is suitable in this situation..(real threading, lack of dbms drivers, etc.).

What platform/language would be most suitable to communicate and exchange data with connected air clients in a local network?

This is my priority list: Cross-platform > easy install > well documented/big community > implemented quickly

Btw: initial sync would take about 0,5 GB to transfer, and an update afterwards about 10 MB.

Solution

Air and Java(backend code) Cross-platform Yes easy install Yes well documented/big community Yes implemented quickly Yes