There are many workspace options for solopreneurs, telecommuters and early stage startups in lots of different neighborhoods. Near MIT, there is the C3 coworking space in the Cambridge Innovation Center near the Kendall Square subway station. Just a short walk away you can find one of the Workbar Cambridge offices on Prospect Street in Central Square. Workbar and WeWork both have locations in Boston proper.
If you are a hardware startup, you might want to consider Greentown Labs near Union Square in Somerville.
If you are into working and rock climbing, Brooklyn Boulders has a location on Dane Street in Somerville.
There are also many coworking spaces scattered throughout the metro Boston areas and nearby suburbs. Some tech companies offer coworking space out of their own facilities, including Verde in Stoughton.