Note: This does not work on OS X Mountain Lion (10.8.2). It has apparently been fixed.

1. On Mac (machine to be controlled)
   1. Open System Preferences (it's in the Apple menu)
   2. Open the Sharing panel
   3. Check the box Apple Remote Desktop
   4. Click Access Privileges
   5. Check the box VNC viewers may control screen with password
      1. enter a password of less than 8 characters
   6. Click OK
2. On remote system (machine to control)
   1. Launch Remmina Remote Desktop Client
   2. Select Connection > New from menu
      1. Select VNC - Virtual Network Computing as Protocol
      2. Fill Server field with either IP address or hostname of the Mac
      3. Optionally fill both User name and Password to make Remmina remember Your credentials
      4. IMPORTANT: Set Color depth to High color (15 bit) or better, otherwise connection will fail
   3. Click Connect (or Save to reuse it later)

The instructions above are for a Linux machine with Remmina installed, but you can do the same from a tightVNC command line (cli or GUI, Windows or Unix). You can also access using other tools like krdc.

• https://apple.stackexchange.com/questions/84221/can-i-remotely-access-my-mac-from-linux-using-screen-sharing
• https://www.lifeonnetwork.com/linux/how-to-remote-from-linux-to-mac/