Need to monitor multiple remote sites

Hello all,
We have multiple remote sites and I have been asked to find a free way to monitor if the sites is up or down. Also need to have a email sent to all techs to alert them when the sites go down. Also send a status email once a day.
Is this possible to do. If so where can I find Nagios documentation on how to set it up.
Thank you
We have multiple remote sites and I have been asked to find a free way to monitor if the sites is up or down. Also need to have a email sent to all techs to alert them when the sites go down. Also send a status email once a day.
Is this possible to do. If so where can I find Nagios documentation on how to set it up.
Thank you