logKext is an older and basically obsolete keylogger which simply records keystrokes and nothing else. It loads into the kernel, so it bypasses user-level security measures and is therefore invisible. On the other hand, in order to install, uninstall and access the program, you must use the command line - a sometimes daunting feat for the uninitiated user.
This application is open source, meaning one can access the source code and edit it. If you are a programmer and want to customize the keylogger to your needs, this could be great. However, for the vast majority of users (even computer-savvy ones), logKext is outdated; the lack of functionality, a user-friendly interface, and accessibility make it an unpopular choice. If you just need a keystroke monitor, try the Perfect Keylogger Lite version and benefit from an easy-to-use free program.