Tunnelblick

Tunnelblick is a free and open-source OpenVPN graphic user interface for macOS. It allows users to manage and configure the VPN connections used by installed OpenVPN clients and remove servers.

History
The first stable release was version 3.0 in March 2010.

Issues
In January 2016, the Sparkle Updater component used by Tunnelblick was found to be vulnerable to a man-in-the-middle attack. This security flaw has since been patched.

Any VPN or third party tool like Tunnelblick can cause connectivity problems while syncing with iCloud.