The Linux Intrusion Detection System (LIDS) is a patch which enhances the kernel's security by implementing a reference monitor and Mandatory Access Control (MAC). When it is in effect, chosen file access, all system/network administration operations, any capability use, raw device, memory, and I/O access can be made impossible even for root. You can define which programs can access specific files. It uses and extends the system capabilities bounding set to control the whole system and adds some network and filesystem security features to the kernel to enhance the security. You can finely tune the security protections online, hide sensitive processes, receive security alerts through the network, and more.
grsecurity is a complete security system for Linux 2.4 and 2.6 that implements a detection/prevention/containment strategy. It prevents most forms of address space modification, confines programs via its Role-Based Access Control system, hardens syscalls, provides full-featured auditing, and implements many of the OpenBSD randomness features. It was written for performance, ease-of-use, and security. The RBAC system has an intelligent learning mode that can generate least privilege policies for the entire system with no configuration. All of grsecurity supports a feature that logs the IP of the attacker that causes an alert or audit.
L4Linux runs in user-mode on top of the µ-kernel, side-by-side with other µ-kernel applications such as real-time components. It is binary-compatible with the normal Linux/x86 kernel and can be used with any PC-based Linux distribution. L4Linux is part of the Dresden Real-Time Operating Systems Project (DROPS) aiming at the support of applications with Quality of Service requirements.
sk98lin is a Marvell Yukon/SysKonnect Linux driver. In the release candidates for Linux 2.6.23, the sk98lin driver was removed under the presumption that the sky2 and skge drivers would be sufficient to cover all hardware supported by the unmaintained sk98lin driver. That presumption was wrong, as several NICs will not work at all with skge and stop talking after an indeterminate period of traffic with sky2.
CinayOS is a 64-bit operating system that was forked from Linux in order to develop a radically different approach to concurrency, SMP, and most other kernel subsystems. Its goals include a new caching infrastructure, easy software package management, and an OpenGL accelerated animation system.