Although they're not required to, some cities and towns open their elections office on Saturday (that is, today) for absentee in-person voting. For example,
- Boston Hours for In-Person Absentee Voting today are 9-2:00 PM in City Hall Room 241 (Congress St. Entrance)
- Cambridge ... on Saturday, November 3rd from 9:00 a.m. until 5:00 p.m.
Google for your city's elections office or your town clerk's office and call them to ask. You can also vote in person on Monday morning if that helps. I believe the deadline for absentee ballot applications is noon on Monday, so you can't do this after that time.
You need to have a reason to vote absentee in Massachusetts, so if you can vote at your regular polling place on Tuesday this isn't for you. However, your reason can be simply that you work in a different city or town and your work hours prevent you from going to the polls. Or, perhaps you work near home but you recently moved and need to vote at your previous location which is too far to get to on a work day.