OnSIP 3.28.2 for Mac was available to download from the developer's website when we last checked. We cannot confirm if there is a free download of this app available. This free software for Mac OS X is a product of OnSIP. Please check the Mac app with an antivirus before launch as it is downloaded from the developer's website, and we cannot ensure that it is safe. The program lies within Communication Tools, more precisely Texting & Video calls.
From the developer:
OnSIP brings your business phone to you, whether you’re at the office, at a client’s site, or working remotely. You can connect with customers, partners, vendors, and coworkers from your OnSIP account on any computer.
With OnSIP, you can take advantage of standard business phone features without any hardware.
You may want to check out more Mac applications, such as sipgate, TRx or Instantbird, which might be similar to OnSIP.