NightGFX is a base graphics replacement available for OpenTTD. It is a 32bpp reworking of OpenGFX in a night-time setting, complete with "working" lights and functional company colors. Mainly intended as a proof of concept and "a fun thing to do", NightGFX is technically complete but could still do with some TLC, including some slight brightening and some variation in the lighting effects. It is only available for download on the online content, but you can also read through the development topic at TT-Forums for some additional information: NightGFX Development.
Source (.7z archive)