VoIP/SIP client (softphone) for Windows

When looking for a SIP and media stack I've spotted libre/librem/baresip from creytiv.com. It has I believe pretty unique combination of simplicity, completeness and most of all permissive BSD-style license allowing commercial and closed-source derivatives.

Console application

Minimal subset (no video support, no codecs besides G.711, just the essentials for voice calls) of libre/librem/baresip as a console application built with Turbo C++ 2006 Explorer. If you're not a Borland products user stay with original source code that can be used with i.e. VC++ 2003.
bsip_tc_20111215.7z - source only

GUI SIP client

SIP client with graphical user interface built upon re/rem/baresip stack. Feature set is very limited, but whole project is self-contained and easy to compile - no external dependencies. GUI is using simplest possible model: single registration account and single call at a time, but application is portable and using configuration from a local JSON file, so many instances can be run simultaneously with different configurations. Each instance takes ~1.8 MB of disc space (including wave files with signals such as ringing).
tSIP: simple VoIP/SIP application

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