Softphonewikipedia
A softphone is a software program for making telephone calls over the Internet using a general purpose computer rather than dedicated hardware.
softphonesoft phonePC-to-PC calling

Comparison of VoIP software

SIP Softphonesproprietary formats
See Comparison of VoIP software
Softphones are client devices for making and receiving voice and video calls over the IP network with the standard functions of most original telephones and usually allow integration with VoIP phones and USB phones instead of using a computer's microphone and speakers (or headset).

Voice over IP

VoIPvoice over IPvoice over Internet Protocol
To communicate, both end-points must support the same voice-over-IP protocol, and at least one common audio codec.
Standards for securing VoIP are available in the Secure Real-time Transport Protocol (SRTP) and the ZRTP protocol for analog telephony adapters, as well as for some softphones.

USB phone

telephony
A softphone is usually used with a headset connected to the sound card of the PC or with a USB phone.
It may be used with most softphones and services like Skype, Sipnet, Sippoint Mini, Net2Phone, MSN Messenger, NetMeeting, Xlite, Skype for Business.

VoIP phone

IP PhoneIP phonesEthernet-based phone
VoIP phones can be simple software-based softphones or purpose-built hardware devices that appear much like an ordinary telephone or a cordless phone.

Session Initiation Protocol

SIPsession initiation protocolSession Initiation Protocol (SIP)
Many service providers use the Session Initiation Protocol (SIP) standardized by the Internet Engineering Task Force (IETF).
SIP phones may be implemented as a hardware device or as a softphone.

Chatcord

It enables the use of a Plain Old Telephone System (POTS) to talk via the Internet away from the computer, after connection is established from the desktop using your specific softphone (such as MSN or Skype).

Telephone

telephonephonetelephones
Often, a softphone 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.
In addition, many computer software vendors and telephony operators provide softphone application software that emulates a telephone by use of an attached microphone and audio headset, or loud speaker.

H.323

RASH.323
VoIP requires a connection to the Internet or another packet switched network, a subscription to a VoIP service provider and a client (an analogue telephone adapter (ATA), VoIP Phone or "soft phone").

Phoner

Phoner and PhonerLite are softphone applications for Windows operating systems available as freeware.

Ring (software)

RingGNU RingRingo
GNU Ring (formerly SFLphone) is a SIP-compatible softphone and SIP-based instant messenger for Linux, Microsoft Windows, OS X and Android.

Linphone

Linphone (contraction of Linux phone) is a free voice over IP softphone, SIP client and service.

MicroSIP

MicroSIP is a portable SIP softphone based on the PJSIP stack available for Microsoft Windows.

Media5-fone

Media5-fone is a VoIP soft phone that uses the Session Initiation Protocol.

Call.center (application)

call.center is a softphone for OS X, Windows, Android and iOS.

Telephone (application)

Telephone
Telephone is a softphone for macOS developed by 64 Characters.

CounterPath Corporation

Its SIP-based softphones, server applications and Fixed–mobile convergence (FMC) products are designed to allow users to make Voice over IP (VoIP) audio and video calls, send instant messages, and manage presence and screen share across multiple devices including desktop computers, laptops, tablets, and smartphones.

Gizmo5

Gizmo
Gizmo5 (formerly known as Gizmo Project and SIPphone) was a Voice over IP communications network and a proprietary freeware soft phone for that network.

Eyeball Chat

Eyeball Chat is a proprietary freeware VoIP, video telephony soft phone with multiple-protocol instant messaging for Windows PCs, produced by Eyeball Networks in Vancouver, and first released in 2000.

EyeBeam (software)

eyeBeameyeBeam (software)
eyeBeam is a VoIP softphone for Windows that uses Session Initiation Protocol to facilitate voice, video conferencing and instant messaging.

Nuvoiz Communicator

Nuvoiz SoftPhone is a SIP and XMPP based SoftPhone application for Voice over IP and instant messaging.

KPhone

It implements the functionality of a VoIP Softphone but is not restricted to this.

BroadVoice

Customers can make and receive phone calls using an ordinary telephone, IP phone, Softphone or an Android or iPhone cell phone via an application.

Spirit DSP

VideoMost
SPIRIT’s voice and video engines are targeted at various applications – PC and mobile communication applications (softphones, IMS-, Unified Communications and Enterprise Mobility clients), terminal user equipment with IP-connectivity (media phones, IP phones, IP set top boxes, Mobile Internet Devices) and infrastructure equipment (IP gateways, ATAs, media servers, etc.).

Nefsis

Commencing 2004, NewHeights Software Corporation licensed the company’s technology to power presence, IM, and web conferencing features in several softphone products sold under the NewHeights and Mitel brands.