You can download the latest version of the Windows OpenVPN client directly from OpenVPN:
https://openvpn.net/index.php/open-source/downloads.html
Once you have downloaded and installed the client, you then need to extract the config.zip file (generated by Untangle/znetmgr), to the following location:
C:\Program Files\OpenVPN\config
For Mac OSX users, we recommend using Tunnelbick. Heres an artcile on how to download and use it: https://support.zynstra.com/hc/en-us/articles/201790652-How-to-connect-via-VPN-on-Mac-OSX