CAMBRIDGE, MASS. — Extell Development and Equity Residential are currently developing 303 Third Street, an eight-story residential community in Cambridge. It is the first residential community in Boston proper to be marketed with the University Residential Community at the Massachusetts Institute of Technology. New York architectural and design firm Cetra/Ruddy designed the 605,000-square-foot project, which contains 292 rental apartments and 167 co-ops. The for-sale apartments are being marketed exclusively to the faculty, staff and alumni of MIT, Harvard University and Massachusetts General Hospital. High-end finishes of the apartments, which range in size from 1,200 to 1,600 square feet, include glass cabinetry and backsplashes, granite countertops and stone selections. Additions to the project include flexible meeting spaces and a club/library. Amenities include a private dining club, a spa and fitness club, an on-site medical office and an underground parking garage. The development is slated for occupancy this winter.