ShCAD is a 2D CAD program written C++ using Qt framework.

LibreCAD is a 2D CAD drawing tool based on the community edition of QCad. LibreCAD has been re-structured and ported to Qt 4/5 and works natively cross platform between OSX, Windows and Linux. It can read DWG and DXF files; and it can write DXF, SVG, PDF and more!

sodaCAD is an enterprise level 2-D vector based drafting program used by fashion designers and manufacturers to create and grade patterns used in the apparel industry.

Vector based CAD library

Open source patternmaking software.

Geomentry calculations and collision detection in C++

c++ port of truetype-tracer (font to G-code/DXF converter)

AGG Anti-Grain Geometry Library

engine

Valentina is patternmaking software for Linux, Windows, and OSX. Download builds from here:

A program that creates handwritten text from a typed text by simulating user's own handwriting

A fast algorithm for finding the pole of inaccessibility of a polygon (in JavaScript and C++)

Fast and lightweight class for Bezier curves of any order in C++

C++ SVG library

An interactive program for creating polygons and determining if a given point is inside or outside the polygons