I have a .NET app that must send data to a Zabbix server. How to do that?
Depends on what you want to do. A good place to start would be here.
One very simple way to do it would be via a console program, since Zabbix supports running console programs on Windows - the return value is the output of the program. Another way is to have Zabbix request a HTTP page containing values you want to monitor.
But again, it really depends what you are trying to achieve.
zabbix_sender is a command line utility for sending data to a remote Zabbix Server.
zabbix_sender -c /etc/zabbix/zabbix_agentd.conf -s
Monitored Host'' -k
mysql.queries'' -o ``342.45''
http://www.zabbix.com/documentation/1.8/manpages/zabbix_sender
Translate the PHP or Ruby code to .NET,
http://www.zabbix.com/wiki/doc/api
I took a look at the PHP code and it seems that Zabbix exposes its API via JSON web service. So such code can be translated to .NET code without problems. You just need some time.