The 2.4-hf kernel tree which only contains hotfixes for 2.4 mainline kernels. These are intended for people who cannot upgrade for various reasons, and who still need to apply a security or stability fix. All patches in this directory are extracted from the next mainline release or pre-release.
The 2.4-wt tree, which is an overloaded kernel that I use on all my servers and stations, as well as some of my employer's servers because of some useful security addons it includes (PaX, Netfilter, Openswan, loop-AES, ACL, lm-sensors, ...). These are normally not recommended for inexperienced people as they might not be as stable as the standard kernel, and might require some tweaking.
a copy of 2.4 mainline kernels, for reference only. This is not an official kernel mirror at all, and you're discouraged from downloading any official kernel from this site. They're still there because they have helped relatives, but may not stay in the future. Please consider downloading from one of kernel.org 's mirrors.