How to keep files in sync between multiple computers?

Let's say you have four computers: A, B, C and D.

Here are what you should do:

1. Install Beyond Sync on all of them
2. Pick up one server as "central server", for example: B
3. On server B, please create three two-way tasks for other three servers: B_folder <-> A_folder, B_folder <-> C_folder, B_folder <-> D_folder
4. On A, C and D, create a single two-way task on each of them to synchronize files with B

The configurations work like:

       B
  /    |    \
 A    C    D

When you added a file in C for example. This file will be synced to B first. Then, B will send this file to A and D. Thus, all computers have the same file.