Is there any possibility to port Freertos to this compiler. Because I have a licenced copy of Hitech PICC18 compiler. Someone said this is impossible because of lack of stack access. Is there a way to implement this :)

I cannot give a definitive answer as I am not familiar with the Hitech compiler. If the compiler does not allow stack access – even from inline assembler – then a port would require some files to be written in assembler. In particular the save and restore context would require an asm file.  Also entry to some functions may require asm wrappers that just call C files (as per the SAM7 IAR port). There will be a new PIC port available shortly that uses the wizC/fedC compiler. Regards.

SDCC group is working on a PIC version of their compiler as well — not sure when it will be out.