A workstation running some flavor of UNIX like Solaris, IRIX, GNU/Linux, BSD, Mac OS X. GRASS also runs on on Win32 within the Cygwin environment. As a minimum, you should have at least 500 Mb for data and 32 Mb RAM. However this will allow you only a very limited usage of GRASS (although see here for GRASS on handhelds). For a serious usage of GRASS you will need 128MB at the very least. Obviously, a good video card is a must for cartography, ideally with 3D support.
C-compiler (cc, gcc, egcs, ...)
GNU make is recommended
zlib compression library (already installed on modern systems)
It is used to internally compress GRASS raster files: libz: http://www.gzip.org/zlib/
lexical analyzer generator (flex),
(lex is no longer supported, please use flex instead) - flex: http://www.gnu.org/software/flex/flex.html
parser generator (yacc, bison)
libncurses4.x/5.x (already installed on modern systems)
dgm/gdbm (dbm.h): GNU dbm is a set of database routines that use extendible hashing and works similar to the standard UNIX dbm routines. Currently not required.
X11 window system for graphical output, development libraries (X development libraries, in some linux distributions they are separate packages)
(winGRASS: As alternative a generic MS-Windows driver is under construction which does not require X11)
Tcl/Tk 8.x libraries (they include 'wish') to use TclTkGRASS Interface and to compile src.contrib/GMSL/NVIZ2.2/
Mesa-3.x (openGL clone) required for NVIZ2.2 (if your OS / graphic card libraries don't come with own OpenGL libraries)
FFTW (library for computing the Discrete Fourier Transform) required for i.fft and i.ifft modules
LAPACK / BLAS (libraries for numerical computing) required for GMATH library (GRASS numerical lib)
http://www.netlib.org/lapack/ (usually present in Linux distros)
Note: the support is intended for future module implementations
libpng (for r.in.png, r.out.png), usually already installed.>
libjpeg (for r.in.tiff, r.out.tiff), usually already installed.
libtiff (for r.in.tiff, r.out.tiff), usually already installed.
libgd (for PNG driver), preferably GD 2.x.
netpbm-tools/libraries (for r.in.png/r.out.png), usually already installed.
(please look at any decent software mirror near you!)
PostgreSQL libraries (for the PostgreSQL database interface)
Unix ODBC (for the ODBC database interface)
Only required for "xanim" and "ogl3d": the Motif or Lesstif libraries
r.in.gdal requires GDAL - Geospatial Data Abstraction Library
R language (for the R language interface)
FreeType2 (for d.text.freetype)