There were two 64 Emulators around the time of the A500/2000 that used cables/boxes to hook up 1541 drives so you could load software. This was really the days before disk images. They figured many C64 owners looking to upgrade would not want to lose their old software and files when moving to a new Amiga 500.
These two are 64Emulator2 which used a Cable it came with, 25pin on one end to hook to the Amiga and the Commodore Seriel on the other to plug into the 1541.
A64 came with a box, 25pin on one side to plug into the amiga and a Commodore Serial port on the other to use with the cable the 1541 would have come with. On the Amiga side both used the Parallel port.
64Emulator2 was the older of the two. It was prevalent when the A500 was first released but was nut updated from that time.
A64 was the newer and when it came out in a run between A64 and 64Emulator2 was considered better.
Both are very old and therefore their compatability are not as good as the newer ones and running on faster/AGA/or later than 1.3 systems might cause unexpected results. They were prevalent enough, however, that some of the newer ones will allow you to use their hardware to connect up 1541 drives.