This is the A1200 version of the Action Replay, which connects into the trapdoor slot of the A1200. This effectively means you can't use a RAM Card or accelerator with the A1200 at the same time. The Action Replay also has no provision for adding any extra RAM. This device allows the user to freeze the computer at any point, and a new display opens. From this display the user can view the memory contents, cheat in games, rip sound, music and graphics and all sorts of other things. You could also make an image of the memory contents and save it to a bootable floppy disks, which if booted from would return your computer to the exact same state when you froze it. This meant the action replay could be used to bypass copy protection in games etc. The Action Replay also offered a slo-mo option where you could slow your machine down to the speed you wanted which could help you cheat in games. The A1200 version included the following features:

Assembler/Disassembler
Watching and Modification of CPU register
Watching of custom chip registers
Memory dumping and modification (in HEX or ASCII)
Memory block copying, comparing, filling and exchanging
Saving/Loading memory from Floppy or HardDisk
Find value in memory
Find instruction in memory
Breakpoints
Graphics ripper
Step Tracing and Trace-to-address
Patching of exception vectors
Basic DOS commands: cd,dir,del,copy,format,setmap
Calculation of BootBlock checksums
Trainer functions
PAL/NTSC switching

Thanks to Gavin Fance