Macs come with ARD (Apple Remote Desktop) clients built-in. The management software for it, however, is $299 for 10 systems, and $499 for unlimited.
VNC is free, however, and you just need a server program, like this.
Once your network is properly configured, you can access your mac from anywhere in the world that has internet, using a standard VNC client.
You can also configure the built-in ARD client to act as a VNC server.