[thelist] Website monitoring software assistance?

[Jonathan]

Howdy List!

We're looking to set up a free website uptime monitoring service for our
customers, but I'm not really finding too much out there to help us out.  Of
course I've looked at the uptime software in the marketplace, but it's
really designed for an IT team looking to monitor groups of services or
groups of services.

We want to set up a service to do website monitoring.  Things like:

http
httpd
pop3
smtp
ftp
imap
telnet
dnsa
dnsns
match
Ping

And we're hoping to do it on an open source budget.  Right?  Well, I know
it's nuts but there must be something out there that's designed more as a
service than for an engineering department.  We're hoping to set up a free
version of what these companies do:

http://www.watchmouse.com/en/index.php
http://www.nmsalert.com/
http://netwhistle.com/overview/default.aspx

We've basically got a very large network of server computers running at 99%
unused capacity (distributed DNS mostly), and figure it would be a good way
to promote our business while giving back to the Net.  

Is there anything out there?  We speak Java, PERL, and PHP, Unix (Linux,
FreeBSD) as well as several page languages, but definitely no Windows and
very little Cold Fusion.

Thanks in advance!

Jonathan