A supertask assembly web, or SAW, is a large array of universes arranged within the multiverse such that their proximity provides strong field gradients in the extrauniversal space in which machinery can be constructed.
Due to the complicated geometry of the multiverse that varies greatly over large scales, these universes may be very far apart and moving rapidly; to circumvent this, arrays are made very large such that from the point of view of an observer inside a universe there are always at least two universes in the array in contact.
Such machinery, being located in extrauniversal space, can operate arbitrarily fast compared to machinery inside the universe, up to and including performing supertasks - hence the name.
This machinery can have several purposes. One is the production of vast numbers of gliders - a typical glider takes a very long time to construct from inside the universe due to the field perturbations needed to create it, but a SAW can produce them almost instantaneously.
Another is power generation, which is often used to drive the SAW itself. Existing in extrauniversal space, a SAW can safely disassemble universes by inducing a phase change and then collecting the released energy (pre-SAW technology can perform similar things, but is significantly less reliable and efficient).
A third purpose is computation - a SAW can perform operations arbitrarily quickly. For a civilisation that values computation, this represents an infinitely large source of value.