Real estate sources tell TMZ ... sitcom creator Jeff Franklin is moving on and is inviting buyers who are interested to make an offer ... buyers, that is, who have $85 mil to spend.

The house sits on the land where the Manson Family slaughtered Sharon Tate, Abigail Folger, Steven Parent, Wojciech Frykowski and Jay Sebring back in 1969. The house was razed in 1994 and a new mansion was built in its place.

There's more recent history ... Jeff hosted the reception at his home for Bob Saget's family after his funeral last week.

The home is 21,000-square feet with 9 bedrooms and 19 bathrooms and sits on 3-acres, with a jetliner view of the city.

The modern estate is decked out with a movie theater, spa, gym, hair salon, billiards room and a bar ... and the backyard features a 75-yard pool with 3 waterfalls, 2 Jacuzzis, a 35-foot water slide, swim-up bar, private grotto, koi pond, lazy river, cabana, BBQ area and fire pits.

Oh and we didn't mention the detached guest house and an underground garage with room for 16 cars.