Home page: http://figurine.sourceforge.net/figurine/
Sourceforge page: http://sourceforge.net/projects/figurine/
Figurine is an alternate editor for the (x)fig format.
Home page: http://www.linuxbrit.co.uk/geist/
Geist is a vector graphic editor with emphasis on raster objects (alpha-transparency, etc..).
Home page: http://www.levien.com/svg/
Sourceforge page: http://sourceforge.net/projects/GillGill is an experiment in developing an entirely SVG-based vector graphic editor, based on the GTK toolkit. It attempts to support all the related standards (DOM, CSS).
Home page: http://www.gyve.org/
GYVE (for GNU Yellow Vector Editor) is an FSF sponsored vector graphics editor that originated in conjunction with GNUSTEP, but now seems to be migrating to Gtk.
Home page: http://www.ivtools.org
Sourceforge page: http://sourceforge.net/projects/ivtoolsivtools is a collection of vector graphics editors that augment idraw with scripting, multi-frame editing, and graph editing.
Home page: http://www.ntlug.org/~ccox/impress/index.html
ImPress is a Tcl/Tk based vector graphics editor.
Home page: http://www.cs.uu.nl/~otfried/Ipe/
Ipe is a vector graphics editor with a focus on extendability via plugins.
Home page: http://wwwiti.cs.uni-magdeburg.de/~sattler/killustrator.html
Killustrator is the KDE vector graphic editor (part of the KOffice suite). It supports many Illustrator-inspired features, like gradient-fills and path-alignment.
Home page: http://sketch.sourceforge.net
Sourceforge page: http://sourceforge.net/projects/sketch/Sketch is a vector-graphic editor written mostly in Python. It supports many Illustrator-inspired features as well (gradient-fills, path-alignment, etc.).
Home page: http://sodipodi.sourceforge.net
Sourceforge page: http://sourceforge.net/projects/sodipodi/Sodipodi is yet another GTK based vector-graphic editor. It can load and save in SVG format.
Home page: http://bourbon.cs.umd.edu:8001/tgif/
Tgif is a mature vector-graphic editor with gratis licensing.
Home page: http://www-epb.lbl.gov/xfig/
xfig is the grand-daddy of all X11 vector-graphic editors.