Just wanted to mention that the or-tools constraint solver is absolutely top notch. It has been winning top3 places in the minizinc competition ever since it entered a few years ago, and placed first in 3 out of 4 categories last year. I've used it quite a bit, and with a few exceptions I've found its completeness relative to the Global Constraint Catalog to be excellent, especially so for open source software. Now if only they had a functional 3 dimensional Geost constraint :)