RADIUS can respond to authentication requests based on its own user account database, or it can be a front end to another database server, such as a Structured Query Language (SQL) server or a Windows domain controller (DC). The DC can be located on the same computer as the RADIUS server or elsewhere. In addition, a RADIUS server can act as a proxy client to a remote RADIUS server.
Avast SecureLine and Avira Phantom VPN are run by antivirus companies as complements to their primary businesses. These services are also limited to Windows, Mac, iOS and Android and don't work without client software. But they offer few features, have a couple of dozen servers at most and don't let you pay anonymously. However, the companies are known quantities, and the services are handy for occasional travelers.
That attitude to the safety and privacy of personal data creates an enormous online security risk. Public Wi-Fi networks, which are ubiquitous and convenient, are unfortunately also highly convenient for attackers looking to compromise your personal information. How do you know, for example, that "starbucks_wifi_real" is actually the Wi-Fi network for the coffee shop? Anyone could have created that network, and they may have done so in order to lure victims into disclosing personal information over it. In fact, a popular security researcher prank is to create a network with the same name as a free, popular service and see how many devices will automatically connect because it appears safe.