download page (http://sourceforge.net/projects/springrts/files/springrts/)
If you have DLed an archive into ~/Downloads/spring_91.0/*, you unpack it and:
[code]name@computer:~$ cd ~/Downloads/spring_91.0
name@computer:~/Downloads/spring_91.0$ cmake ./
name@computer:~/Downloads/spring_91.0$ make[/code]
and you've got a working version.
spring_91.0 contains both 'spring' and 'libunitsync.so'.
if you move the archive to any folder (for example ~/.spring/engines/) and simply do cmake and make (without make install), you only have to relink your lobby to these two files when you join a host with a different engine.
How you do it or if it does it automatically, is another topic.