There were a number of 3rd party upgrades offered for the 128k and 512k Macs, particularly as the Plus was released. This page tries to document some of them.
MacMemory, Inc. Max2
The Max2 from MacMemory, Inc. replaces several chips on the motherboard with sockets, and then there is a daughter board that fits in place over the system memory. The daughterboard contains sockets for additional memory chips, 2MB populated, and supporting up to 4MB. It does not use 30pin SIMMs like the Plus and some other 3rd party upgrade boards. Originally this upgrade was typically offered as a replacement logic board with the upgrade already installed, since installation involved desoldering original chips, but it could be purchased as a self-installed kit.
The important thing to check when installing this or servicing a mac with this installed, is to check the 5V voltage, adjusted on the analog board. The additional load can drop the 5V line too low.
MacMemory, Inc. MaxPort
The MaxPort was a SCSI upgrade product by MacMemory, Inc. There were two boards in this upgrade, connected by a ribbon cable. The first board sat in the ROM sockets, and the ROMs were placed in sockets on this board. Then a ribbon cable went to a board that was typically mounted on top of the floppy drive, which contained the SCSI controller and additional logic. From there, a ribbon cable went to a DB25 connector that replaces the battery door on the back case.
MacMemory, Inc MaxChill
This was a piezoelectric fan with 2 clips to provide power. It was quiet and helped the convection cooling of the Mac. It was generally recommended when a Max2 or MaxPort were installed.
The MacSnap came in 2 varieties: 1MB and 2MB. It was a large board that fit over the top half of the Mac's logic board, and used DIP memory, like the Max2, not 30pin SIMMs.
More information from vintagemacworld
Again, it is important to check the 5V voltage of the Mac after installing or servicing.
Dove MacSnap SCSI
The MacSnap SCSI was a daughterboard that sat in the Mac's ROM sockets, with the 2 ROM chips plugging into that. The daughterboard also contained the NCR SCSI controller, and a ribbon cable that wound through the chassis, and connected a DB25 connector that replaced the Mac's battery door on the back of the case.
Computer Care MacRescue
The MacRescue board was a full 68000, SCSI controller, and 30pin SIMM RAM upgrade card that used a KillyKlip to sit on top of the system's 68000 processor.
Perhaps one of the most interesting aspects of this upgrade is it takes up to 6MB of memory (6x1MB 30pin SIMMs). Although the Mac can only use 4MB of the RAM for system memory, the other 2MB can be used as a RAM disk with software originally included with the board.
Originally retailed for $319 in 1990 without the necessary 128k ROMs. ROMs were an additional $149 from Computer Care.
If anyone has documentation on the DIP switch and the RAM disk software, please update this page.