Njam is available for various operating systems:

System requirements for Windows version
System requirements for Linux version
Minimal versions of popular Linux distributions are:

Linux notes

The provided .tar.gz file is a simple zipped package. Unpack it to some directory, and run the njam executable. If you do it from shell, it would go something like this:

tar -xzf njam-2.00-i386.tar.gz
cd njam-2.00-i386

You don't need to install it, and you don't need to be root.