Tragofone - White-label VoIP Softphone with WebRTC and Auto-provisioning
SMS Plus - SMS Plus app offers features that let you forward text messages through internet connection as well as through other social media platforms.
tSIP - tomeko.net/software: SIP client for Windows.
PhoneLeash: SMS/MMS forwarding - PhoneLeash: SMS/MMS forwarding app offers features that let you forward your desired text messages and multimedia messages to your email or your other mobile phone so that you can access them later.
YakYak - Desktop client for Google Hangouts
Easy Message - Easy Message app comes up with features to help users in effortlessly sending text messages to a phone number, which is not in the contact list.