DOWNLOAD: The source code as a compressed archive on the code page https://sourceforge.net/p/fosforcms/code/.
Do you want to help developing and improving this little CMS? Contact me per Email to [jenswagner20 AT ovi DOT com] and I'll give you more details. If the community grows, I'll open a developers forum on fosforito.net!
Note: please do not use this software for public websites. It is not very secure and some features are missing, not completly developed or disabled...