Linux lacks a good key remapping solution. In order to achieve satisfactory results a medley of tools need to be employed (e.g xcape, xmodmap) with the end result often being tethered to a specified environment (X11). keyd attempts to solve this problem by providing a flexible system wide daemon which remaps keys using kernel level input primitives (evdev, uinput).
I'm thankful somebody appears to have taken this on on linux! The last time I tried to switch to linux, the lack of a good key remapping program was not helpful.
I haven't used it but will try it the next time I try out a switch
See also kanata
Found via news.yc