
Romuald writes about our earlier RFID post:
I just read the latest post about RFID development. I just let you know that it already exists Free/Libre projects in this area.
- Proxmark which is a famous tool to sniff, learn, tweak, spoof many kind of RFID.
- WIP mikeycard which will be a tool useful to clone a MIFARE Classic tag and emulate passive RFID/NFC tags.
Update, from the comments:
I forgot to talk about OpenPCD that use librfid which is Free/Libre hardware and software too.
And maybe someone could be interested in libnfc which is a Free/Libre library to drive NFC chips (currently on the proprietary PN53x chips).
Thanks for the tip!

I forgot to talk about OpenPCD (http://www.openpcd.org/) that use librfid (http://openmrtd.org/projects/librfid/) which is Free/Libre hardware and software too.
And maybe someone could be interested in libnfc (http://libnfc.org) which is a Free/Libre library to drive NFC chips (currently on the proprietary PN53x chips).