For example, php-based(: or linux shell script or perl-based, ...) tool
like phpsysinfo(: http://www.**-**.com/ ) displays things
like Uptime, CPU, Memory, SCSI, ...
But it doesn't supports email alert function(: forward above summary to
administrator with html format).

Does Anyone knows such free tool?

Try NAGIOS .. its probably already loaded on your linux distribution.
If not, you can go here and get all the information and more that you
might need ..
http://www.nagios.org/

You might look at big brother.

It is a client/server program geared primarily for watching
one computer with another, but the client supports email alerts.
We used it to actually send pages to our cell phones when the
server health is in question.

--
Duane Smeckert
google for email
spambots, you should not send email
to  los.ange...@fbi.gov
or  presid...@whitehouse.gov