The kernel comes in source format, extract this on the Linux system, select options and copy. Pre-compiled kernels are available. Cost effective and versatile. Great range of applications which are integrated. Freedom of use, rapid development.
Source code is available to allow bugs to be fixed and then re-distributed.
Lots of applications available. Many server applications including Apache and Samba. ZOPE is a dynamic web application. Monash provides servers for many of these functions. Linux is a good environment to do something new without licensing restrictions.