I am looking for a software that can create a network topology diagram that runs on OSX. Please give me your suggestions. Thank you!
I don't know what do you want exactly, but you can try the lansurveyor.
Discovers and draws topological maps for TCP/IP and AppleTalk networks. Features network node Up/down testing (polling) for both TCP/IP and AppleTalk nodes with alerts, including paging and email.
You might want to try "Zenmap" (an nmap GUI implementation), the download link is: http://nmap.org/download.html The OSX link is somewhere at the bottom of the page.
It’s maybe not the perfect »topology mapper« (though it has a nice clickable graphic mode) but offers a lot of insight due to using nmap »under the hood«.