Brosix Public is a free highly secure instant messaging tool, see link :
It's allow to have text chat, voice chat, video chat, file transfer, all encrypted with industry standard high-security AES 256 bits encryption.
Here you can find the list of feautures :
The program it's already portable as stated on their forum :
Do you think it's possible to make a version to be use on portableapps ?
Thanks for your time.