I'm experiencing the same issue on OSX 10.12.3. Synergy v1.8.8-stable-25a8cb2 works fine, but 1.9.0 rc3 crashes instantly when I try to start it.  Process:               synergy [80543] Path:                  /Volumes/VOLUME/*/Synergy.app/Contents/MacOS/synergy Identifier:            synergy Version:               1.9.0 (1.9.0) Code Type:             X86-64 (Native) Parent Process:        ??? [1] Responsible:           synergy [80543] User ID:               501 Date/Time: