udis

http://udis86.sourceforge.net/

./configure --enable-shared && make && sudo make install

If Factor is still unable to find libudis86 after installation run: sudo ldconfig

If you are using Mac OS X and Homebrew (http://mxcl.github.com/homebrew/), you can just:

brew install udis86

On Arch Linux, you may have to apply this patch:

erg@ommegang ~/src/udis86 $ [master*] git diff
diff --git a/configure.ac b/configure.ac
index 37fe23d..831fff0 100644
--- a/configure.ac
+++ b/configure.ac
@@ -7,6 +7,7 @@ AC_CONFIG_HEADERS(config.h)
 AC_CONFIG_AUX_DIR(build)
 AC_CONFIG_MACRO_DIR([m4])
 
+AM_PROG_AR
 # Make sure $ACLOCAL_FLAGS are used during a rebuild.
 AC_SUBST([ACLOCAL_AMFLAGS], ["-I $ac_macro_dir \${ACLOCAL_FLAGS}"])
 
@@ -25,7 +26,7 @@ case "$host_os" in
 esac
 
 # Initialize the automake subsystem.
-AM_INIT_AUTOMAKE([-Wall -Werror foreign])
+AM_INIT_AUTOMAKE([-Wall foreign])