To build from sources you should install gcc, g++, make tools and ncurses library (development version).

Package names are different in Mac OS X and  different linux distros, but it is easy to search.

Then use command

    $make
    
If build successes go to .libs directory and take *.so (or *.dylib in Mac).
    
In Mac OS X you can build a universal binaries (fat dual-exe binary: contains x86 and x86_64 both).
To do this add to makefile's CFLAGS and LDFLAGS next options:

    -arch i386 -arch x86_64
    
( For MacOS X it is important, because mono is 32-bit, but built with default settings libtermkey is 64-bit.
You will be confused when DllNotFoundException will thrown. )

Linux ELF format currently doesn't support fat binaries, but you can cross-compile, for example, 64-bit
image using 32-bit base system. You need gcc-multilib installed. To compile 32-bit binary add

    -m32
    
to CFLAGS or 

    -m64
    
if you want to build 64-bit image.