OpenSC5 is a reverse engineering project for SimCity (2013), also called SimCity 5. Since SimCityPak has become completely dead, this is now the only SimCity-focused program out there.
Parts of it are based on code from SimCityPak, others from other sources, and other parts are completely novel.
A major part that only OpenSC5 does is download the update files from update.prod.simcity.com. Turns out, you can get SimCity for free! (unfortunately it still looks for origin but the data files are still free)