fKeys Warnings
There are some very important things to bear in mind before using fKeys, even though it seems to be working well in the field.
fKeys is a kernel extension; as such, the usual protections that MacOS provides against bugs do not apply, and errors in this code may very well crash your machine. If you're not comfortable with that, do not install fKeys.
fKeys is known to run on MacOS X Tiger on G4 & Intel Macs. The primary development platform is a 15" Core Duo 2 MacBook Pro running the latest Tiger, and it is also tested on a 15" ADB AlBook. If your system is much weirder than these, well, it'll probably work but we can't promise anything.
Michael Baltaks' DoubleCommand IS NOT COMPATIBLE WITH fKeys, according to one report from the field. It won't work to install both of them. (Thanks to Sorin Paliga for reporting this.)
Still want to go ahead with it? Great! You'll need to choose a version to download, then read the installation instructions.