The purpose of anonymizers is to make online activity untraceable for users.
Anonymizers are proxy servers that effectively intermediary between the client and the actual server. Anonymizer attempts to provide a shield of anonymity by protecting the identification information of the existing systems using the service or resources.
Various types of anonymizers are available freely and commercially on the Internet. Protocol-specific anonymizers only understand a specific protocol and can only mediate connections that use that particular protocol.
This works because the client would initiate a connection to the anonymizer. The commands that are sent to the anonymizer are shipped inside a message.
After receiving the command, the anonymizer would strip out the commands and relay the connection information to the destination server as if it originated from the anonymizer.
There are protocol-independent anonymizers, which effectively tunnel the traffic between the server and the client. The protocols used by anonymizer services include OpenVPN, PPTP, SOCKS4, SOCKS5, etc.