The Taxonomy Nested Intervals module maintains a list of nested intervals for taxonomy terms. It is fully multiparent compatible.
This module is useful for large vocabularies. It is similar to Taxonomy Edge, but uses a different technique.
They each have their strength and weaknesses. For very large vocabularies that change very seldom, I would probably recommend Taxonomy Nested Intervals as this module can be a bit more heavy during insert/update than Taxonomy Edge. The Taxonomy Edge module, however, provides an easier data model for custom queries.
There's also the Taxonomy Lineage module, which uses a "materialized path" technique.
Provides overrides for the taxonomy/term/% page (incl. feed) and also reintroduces the /all depth modifier. There's a patch bundled with the module, which allows global override of taxonomy_get_tree().
Views integration is also available through the submodule Views Taxonomy Nested Intervals
Implementation description
Attempt at nested intervals implementation. I view this as a mix between materialized path and nested sets.
(Nested sets, farey fractions, matrix encoding, möbius transformation, etc).
Essentially, the process is to take an enumerated path and turn it into a unique fraction.