The included 6502 Assembler "A65" can be found at http://osi.marks-lab.com/software/tools.html
the included disk creation tool can be found at the same place.
You can compile these tools on Mac/Linux as well

To create .lod file for video based OSI computers C1/C4/C8 (65V) use the folloing command
a65 -b -O disktool.asm

To create .65A file for serial based OSI computers C3 (65A) us the following command
a65 -b -A disktool.asm

To create assembler listing use the command
a65 -L -p0 disktool.asm  > disktool.txt

To create bootable disks OSI dump images
bootthis -5 -l0300 -e0300 -o disktool.bin DiskTool5.65D
bootthis -8 -l0300 -e0300 -o disktool.bin DiskTool8.65D