An elegant, easy-to-use and full-featured SIP client with:

messaging, audio and video transfer, fast file transfer, conference support, multiple accounts, encryption (TLS/SSL and sRTP)

as well as:

SoftPerfect WiFi Guard is a great app for tracking strangers and various devices on your local network. Modern Wi-Fi networks are generally well protected, but there are a number of weak points that can compromise your Wi-Fi password; these include encryption vulnerabilities and brute force attacks. As a result, someone can gain unauthorized access to your Internet connection and local network and use them without being noticed.

WiFi Guard will warn you if your network is being used without your knowledge.