ALS Prolog was the commercial offering of Applied Logic Systems Inc. until about 2012, when it was open sourced on GitHub. The version described at ALS Prolog is the original 32-bit version. A workable 64-bit version can be built which lacks gc and indexing. However, 64-bit address space is so huge, and modern machines so fast, that very large prolog programs can be run efficiently with the system.
The build tree for open source ALS Prolog is available on GitHub. Downloading the tree and following the directions in the README.md file will build ALS Prolog for 64- or 32-bits, according to the system it is built on.
Extra development hands are welcome.