Yes you can use this software and can made changes. You can distribute the modified version, but condition is that you must provide the source code with the modified version.
Veritas wrote:
I can install it localy, and use it in ex. an office for internal communication without any cost?
Yes u can install it locally or in your office without any cost. It is FREE.
Yep, you can use Wildfire absolutely for free. Of course, we hope that you like it so much that you’'ll want to try out the commercial extension, Wildfire Enterprise: http://www.jivesoftware.com/products/im/
It has some great features and also gets you professional support.