The Free Pascal Compiler (FPC) is open source and the successor of Borlands Turbo Pascal. Sources and infos can be found on www.freepascal.org
I started the initiative of the porting of FPC in August 2023. Luckily I could convince Michael Grundlitz for the first porting efforts.
You can follow the development here:
Download FPC for RISC OS (alpha 0.5)