Can I use open source OpenVPN client GUI to connect to the access server

Yes, you can use any OpenVPN Community client to connect to OpenVPN Access Server, provided that the client software supports OpenVPN version 2.1 or later. For instance, the Tunnelblick for Mac OS X can be downloaded from and used with OpenVPN Access Server. Once the client software is installed on the user’s computer, the user can login to the Access Server’s Connect Client to download a customized client configuration file. That client configuration file must be placed in the proper directory for the OpenVPN client software in question.