Complex sentence: I've invented and/or implemented key features of the NRHP list-article system, which paid off well enough for the system to be featured in the September 2012 Wikipedia-Loves-Monuments photo contest.
Split into simpler sentences: I've invented and/or implemented key features of the NRHP list-article system. The system to be featured in the September 2012 Wikipedia-Loves-Monuments photo contest.