And what about an hardware project of a full PLC, ready to be used ?

It's planned, and even actually available. Physically, it looks like the inputs/outputs modbus module already existing (same case).

Update middle of year 2013: prototype tests successfull, it is working perfectly! people interested can contact me...

If you are interested for hardware, with more than just a slave I/O module, but with a real autonomous PLC, the survey is always opened here :

Here are the main features planned for the future PLC :
- Processor x86 at 300 Mhz, 128 Mb of RAM, CompactFlash of 128 Mb, Real Time Clock with backup included.
- Ethernet 10/100Mbits (RJ45)
- Serial port RS232 (DB9, Signals Rx/Tx only) - 2 more internals (not normally available)
- RS485 link (2 points terminal, half-duplex)
- Two USB 2.0 ports type A "master" (one internal)

- 12 digital opto-isolated inputs (9VDC to 24VDC power common)
- 8 digital opto-isolated outputs (48V, 100 mA maxi, two commons independants - per 4 outputs group)
- Quality connectors with Phoenix Contact terminals (5.08 mm)
- 1 user Push Button (that can be used in the prog to ack defaults, give an order, ... ) and a green LED for user information (also to be used in the prog).

- Power input from 9VDC to 24VDC (on jack or 2 points terminal). Switching regulator for better efficiency.
- Possible fixation on DIN rail.
- Dimensions: Width 157mm, Height 86mm, Depth 58,5mm.
- Electronic components in DIP packages (if nedded, for easier manipulations). IC on supports.

- Real-time managed with Xenomai. Linux kernel 2.6.38 "mainline" (standard PC without specific patch) - ClassicLadder embedded version software.
- Programming (free) software 'ClassicLadder' tool running under Linux and Windows - no specific cable required
- Monitor link to connect to the PLC, in IP on ethernet, and in serial RS232.
- Modbus/master on RS485 link for connection with inputs/outputs modules (not real-time).
- Modbus/TCP server (slave) included (for link with Scada).

Anticipate a price of 249 euros to get a model of this PLC done and tested by myself.

If you are interested by an "open" PLC, based on free software and running on Linux, contact me !