WOuldn't that be similar to "guest house"? Anyhoo, I googled the terms.
The good ol' AARP had this article: http://bulletin.aarp.org/yourworld/yourhome/articles/long_live_the_granny .html
Googling three of the companies/providers mentioned: http://www.google.com/search?hl=en&q=%28%22Cobblestone+Homes%22+OR +% 22Western+Homes+Corp%22+OR+%22Precision+Integrated+Homes+%22%29
Thre is also what IIRC is called "universal housing", that combines aspects of handicapped-accessibility. Basically, for older folks, key things seem to me (as I myself age) ease of maintenance, reachability, ease of movement within the space (open plans tend IMO to be easier to get around in), and basic safety (avoid things liek sunken living rooms and otehr level-changes, grab bars in bathrooms, and the like).
A lot of small-space living ideas are applicable, really, with *efficient use* of space being much more important than merely lots of space. I have lots of space in the current place, and very little of it is *efficient*. OTOH, the rental house I'd been in had lots fo good stoarage that was easily accessible (older home, obviously).
I think that, for older folks looking to "unload", built-in storage becomes more important, in part because it means they don't have to have as much furnitrue, and second because built-ins, *esp.* with doors!, are so much easier to maintain, unlike furniture which collects dust and has to be kept-up with.
I'm not sure what type of info you're looking for, but maybe some of the above will be useful.