Hi everyone, can I monitoring downtime or uptime for last month in %? As in Nagios:

Yes it can with nagioscore3 for example.

I have nagios turning on a raspberry pi and monitor over the 100 IP-addresses (devices)

For axample here a configuration file from nagios

###############################################################################
# SWITCH.CFG - SAMPLE CONFIG FILE FOR MONITORING A SWITCH
#
# Last Modified: 10-03-2007
#
# NOTES: This config file assumes that you are using the sample configuration
# files that get installed with the Nagios quickstart guide.
#
###############################################################################


###############################################################################
#
# HOST DEFINITIONS
#
###############################################################################
###############################################################################

# Define the switch that we'll be monitoring

define host{
use generic-switch ; Inherit default values from a template
host_name 192.97.119.11 ; The name we're giving to this switch
alias XXXXXX AP1 ; A longer name associated with the switch
parents 192.97.119.5
address 192.97.119.9 ; IP address of the switch
hostgroups routers ; Host groups this switch is associated with
notes_url https://192.97.119.11/
}

# Define a service to "ping" the local machine

define service{
use generic-service ; Name of service template to use
host_name 192.97.119.11
service_description PING
check_command check_ping!100.0,20%!500.0,60%
}

# Monitor uptime via SNMP

define service{
use generic-service ; Inherit values from a template
host_name 192.97.119.11
service_description Uptime
check_command check_snmp!-C public -o 1.3.6.1.2.1.1.3.0 -P 1
}



# Define a service to check SSH on the local machine.
# Disable notifications for this service by default, as not all users may have SSH enabled.

define service{
use generic-service ; Name of service template to use
host_name 192.97.119.11
service_description SSH
check_command check_ssh
}


You can monitor voltage, cpu usage, detect port flapping, uptime...