Many of us who live in larger intentional communities first started living together in casually structured, shared households... There are certainly hundreds, if not thousands, of shared households in the United States which self-identify as intentional communities (see Communities directories).
There is overlap between "shared households" with other types of communities. For example, there are Egalitarian communities which occupy a single house, which would probably be considered a shared household by most people. Many Student Co-ops similarly occupy single houses. It is not usual for shared households who self-identify as Intentional Communities to label themselves as Cohousing. This is not consistent with the more common image of neighborhood-level cohousing (see Not cohousing).
In late 2012, the Cohouseholding Project was created to define and promote a model of more sustainable shared households - households which are more sustainable socially, environmentally, and economically.
There are many non-profits and programs within non-profits which are dedicated to encourage home sharing. Home sharing "dyads" rarely self-identify as "Intentional Communities." Many of the agency-supported program focus on pairing seniors, who often own the home in question, with younger people. Its generally presented as a way to help support the senior in remaining independent, while providing the younger person/family with high quality living space at a low cost.
National Shared Housing Resource Center has a directory of organizations all over the US that support home sharing.