You can get the current version of FreeModbus at freemodbus-v1.6.zip. This versions includes Modbus RTU/ASCII, Modbus TCP, input/holding register access, discrete registers and more. In addition it has been ported to the following platforms: FreeRTOS/Cortex M3 SAM3S, FreeRTOS/ARM STR71X, FreeRTOS/ARM AT91SAM7X, lwIP/PPP/STR71X, Freescale MCF5235, lwIP/MCF5235, Atmel AVR ATMega168, TI-MSP430, Win32 and Linux.
If you want to take a look at the source you can find information on how to access the GIT repository at https://github.com/cwalter-at/freemodbus.
FreeMODBUS is provided free of charge by SILA Embedded Solutions GmbH.