www.zabbix.com/download.php
First, install xcode. I know, groans abound, but it's required so just do it unless you feel like you want to trust my binaries. Secondly, grab the zabbix source code, it's free and relatively small.
Next, follow the sequence of steps exactly, it is easy, fast and relatively pain-free. From a shell as an administrative user:
Install command-line tools:
userownloads user$ xcode-select --install
Untar/uncompress the latest tarball (2.4.5)
userownloads user$ tar -zxvpf zabbix-2.4.5.tar.gz
Switch to the tarball directory
user:~ user$ cd zabbix-2.4.5
Run the configure sсript with the --enable-agent switch
user:zabbix-2.4.5 user$ ./configure --enable-agent
Make the executable
user:zabbix-2.4.5 user$ make
Make the necessary local directories
user:zabbix-2.4.5 user$ sudo mkdir -p /usr/local/etc /usr/local/sbin
Copy the configuration file to the local etc directory
user:zabbix-2.4.5 user$ sudo cp ./conf/zabbix_agentd.conf /usr/local/etc/
Copy the daemon file to the local sbin directory
user:zabbix-2.4.5 user$ sudo cp ./src/zabbix_agentd /usr/local/sbin
Edit the agent daemon file (beyond the scope of this document)
user:zabbix-2.4.5 user$ vi /usr/local/etc/zabbix_agentd.conf
Start the agent, and enjoy!
user:zabbix-2.4.5 user$ /usr/local/sbin/zabbix_agentd