Please note that all information detailed here is specific to Free Pascal 3.x and above. It does not apply to the older AROS Free Pascal 1.x port, nor does it apply to the even older 0.99.x and 1.0.x versions of Free Pascal for classic Amiga/m68k.
However, this port is very closely related to the recent supported classic Amiga/m68k and MorphOS platforms as they share some of the same code with AROS in an attempt to unify the support in Free Pascal for these platforms.
This port is aimed at AROS (AROS Research Operating System), the open source implementation of the "classic Amiga" operating system, which runs on modern processors like x86-32/x86-64/arm and PPC. Currently x86-32 ABIv0 is the only supported target for Free Pascal.
Because AROS is API compatible with Amiga (and binary compatible with Amiga/m68k), there is much similarity when addressing classic Amiga, MorphOS and AROS (all of which are now supported by Free Pascal).
More information regarding Free Pascal for AROS can be found on the Free Pascal 4 Amiga Wiki (under slow and continues development).