From Fedora Project Wiki
Backwards Compatibility
Fedora provides legacy system libraries for compatibility with older software. This software is part of the Legacy Software Development group, which is not installed by default. Users who require this functionality may select this group either during installation or after the installation process is complete. To install the package group on a Fedora system, use Applications > Add/Remove Software or enter the following command in a terminal window:
su -c 'yum groupinstall "Legacy Software Development"'
Enter the password for the root account when prompted.
Compiler compatibility
The compat-gcc-34 package has been included for compatibility reasons:
https://www.redhat.com/archives/fedora-devel-list/2006-August/msg00409.html
KDE3 development
Refer to Docs/Beats/BackwardsCompatibility/KDE3.