There are several out there., a couple on sourceforge. http://layout.sourceforge.net/links/index.html lists most of them. LayoutEditor has nice features and good for MEMS work but can't cope with large designs. Toped has limited functionality. Glade is good (listed as a broken link but isn't) and runs on windows, linux and solaris. Electric is showing its age.
well as i see Editors can be any.. its the LVS etc. part(later stage) which is important....and cedense is gud in that..
but if u have worked on magic, default visuals of cadences will look v.bad....