Models:
All of the Necron infantry are from Rebel Minis The Scourge line; Necron vehicles are kitbashed from GW Necron and Eldar bits, plus some plasticard details (destroyers and Canoptek Spyder use one of the Eldar command vehicle sprue bits; destroyer torsos are from Khurasan's federal security robots); the scarabs are Reaper Bones beetle swarms; the Wraiths use 2 GW Necron Scarabs each, with some guitar string and plasticard details.
Chaos Iron Warriors are Prydian Knights from the Ion Age; cultists are Khurasan Andromedan Cultists; Bloodletters and Furies are from Magister Militum's Blood Dawn range; Plaguebearers and Daemonettes are from Daemonworld; Nurglings are from Khurasan. The Daemon Prince and Bloodthirster are converted GW Chaos Possessed and Bloodletter models, respectively.
Predators and Vindicator are converted from Rebel Minis Earth Force APC and Titan APC (IIRC); Leman Russ are from Proxie Models, and the Reaver is from Dreamforge, with a few 40K bits added.
The project started out as just a modeling challenge I made to myself: to see if I could closely approximate a larger model in 15mm scale while doing it the old-fashioned way (i.e., kitbashing instead of 3d CAD modeling). I don't have any great love of 40k, but it's one of the more recognizable settings to toy with and, at least for Necron and Eldar vehicles, lots of GW bits suggest forms and parts of the original models. For the infantry models, I just went with the closest approximation without needing to modify them.