GWorkspace
GWorkspace is the official GNUstep workspace manager. It is a clone of NeXT's workspace manager and already ready for daily usage.
GWorkspace is probably one of the most useful and usable workspace managers available on any platform, owing to its well-designed interface and the natural, consistent design that it inherits from the GNUstep framework.
Please see its homepage or the GWorkspace User Guide for more information.
Additional Inspectors
IMImage
IMImage image Inspector for GWorkspace.app to preview many types of graphics formats not supported by NSImage utilizing Image Magick. The following graphics formats are currently supported: art, bmp, cgm, eps, fig, fpx, hpgl, ico, miff, mng, mvg, pbm, pcd, pcl, pcx, pgm, pict, pix, pnm, ppm, psd, rla, rle, svg, tga, wmf, wpg, xbm, xcf, xpm, and xwd. It can also be used to preview Type 1 and Truetype fonts.
SGContentViewer
A contents Inspector that can play Ogg Vorbis, mp3, speex, flac, shorten, voc, midi, and mod files.
RpmViewer
A contents Inspector to see the contents of rpm packages.
VCFViewer
A contents Inspector for VCF files.