The best replacement for shared memory is message passing.

The best alternatives to shared memory are rated as following:
★★★★★  message passing
★★★★  distributed memory
★★★★  dedicated memory
★★★  message queue
★★  memory mapped file
★★  pipes
★  global memory
★  dedicated
★  semaphore
★  ipc
★  mmap
  named pipes
  sockets
  memory map

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Speaking about shared memory, one probably shouldn't forget about semaphores.

Other search terms related to shared memory and their ratings are:
★★★★★ semaphores
semaphore
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shared memory
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