According to Wikipedia, a softphone is a software program for making telephone calls over the Internet using a general purpose computer rather than dedicated hardware; it can be installed on a piece of equipment such as a desktop, mobile device, or other computer and allows the user to place and receive calls without requiring an actual telephone set and it is designed to behave like a traditional telephone, sometimes appearing as an image of a handset, with a display panel and buttons with which the user can interact.

A softphone is usually installed and used with a smartphone, "adding a number" and expanding its capabilities. There are numerous softphones for all operating systems, such as Android, iOS, Windows and Mac, many free, most "freemium" (i.e., can be downloaded, installed and used free of charge but require payment for more advanced features) and quite a few that require a payment from the onset.

While these days smartphones still rule, there are numerous options for laptops such as Windows and Macs.

We find that Zoiper stands out in its support of virtually all platforms and operating systems; however, for some OSs there may be niche apps that could work better and / or provide freely features that require payment on Zoiper. For instance, on Windows there's the free and open source MicroSIP, BareSIP and Groundwire on Android and Linphone on many other platforms.