SrvCheck

SrvCheck is a simple ping-like program, that can check the availability of a remote server using different application protocols. To perform the check, SrvCheck sends a specific request, depending on the type of the server (it will use a HTTP request if the probed server is a HTTP server, a POP3 connection for POP3 servers, etc). Any unsupported protocol based on TCP can be checked as well - in this case, SrvCheck will simply look for a successful TCP handshake. SrvCheck supports the following protocols: HTTP, Gopher, SMTP, POP3, NNTP, FTP, SSH, TCP.
SrvCheck is an opensource program, released on the GNU/GPL license. SrvCheck is available for Linux and Windows.

Download: srvcheck020-linux.zip (Linux)
Download: srvcheck020-win32.zip (Windows)
Download: srvcheck020-src.zip (Sources)

You will find older releases here (although you definitely should use the latest version anyway)