Just the other day me and my friend struggled to exchange a large file between two laptops sitting right next to each other.
Finally we found a flash drive. This program would have saved me a lot of time. Additionally, if I was to write down a list of what I wanted in a LAN messaging client, this would check off all the boxes: instant messaging, public key encryption (AES encryption with RSA as the key exchange), broadcast messages, file transfer, ability to organize contacts, and logging. Best of all it's serverless and cross-platform (Mac/Linux) with no feature-limits on the non-Windows versions.
License: GPL v3 license
Languages: 14 including Spanish, Portuguese (Brazilian), French and Italian,
Screenshot:
Here (too big to directly link)
Will test out hopefully soon.