How do I access the web GUI from another computer?

The default listening address is 127.0.0.1:8384, so you can only access the GUI from the same machine. This is for security reasons. Change the GUI listen address through the web UI from 127.0.0.1:8384 to 0.0.0.0:8384 or change the config.xml:

<gui enabled="true" tls="false">
<address>127.0.0.1:8384</address>

to

<gui enabled="true" tls="false">
<address>0.0.0.0:8384</address>

Then the GUI is accessible from everywhere. You should set a password and enable HTTPS with this configuration. You can do this from inside the GUI.

If both your computers are Unix-like (Linux, Mac, etc.) you can also leave the GUI settings at default and use an ssh port forward to access it. For example,

$ ssh -L 9090:127.0.0.1:8384 user@othercomputer.example.com

will log you into othercomputer.example.com, and present the remote Syncthing GUI on http://localhost:9090 on your local computer.

If you only want to access the remote gui and don’t want the terminal session, use this example,

$ ssh -N -L 9090:127.0.0.1:8384 user@othercomputer.example.com

If only your remote computer is Unix-like, you can still access it with ssh from Windows.

Under Windows 10 (64 bit) you can use the same ssh command if you install the Windows Subsystem for Linux.

Another Windows way to run ssh is to install gow (Gnu On Windows). The easiest way to install gow is with the chocolatey package manager.