BuildCraft can be downloaded through sponsored links, either by adfly or adcraft. Along with donations, sponsored links is one of the only source of revenue for BuildCraft, ensuring that the mod will continue being developed and maintained over months, while remaining freely available to players.
In all cases, download becomes available after 5 seconds of waiting. BuildCraft 2.x and 3.x being distributed in 5 modular files, the total time for having access to a full release should not exceed a minute. While this is certainly an extra burden on the player plate, this minute of your time is really supporting all the work being the mod and is highly appreciated.
Sponsored links may be difficult to follow the first time. On adfly, the download link will be located on the top right corner of the interface:
On adcraft, the download link will be located on the middle on the page:
Thanks again for your time and patience. Looking forwards to releasing new awesome features!