Vans/Buses

Green Passage Transportation LLC, Ken(previously Tony/Frank/etc), 
617-209-2254, contactus@gogreenpassage.com,  http://gogreenpassage.com

MIT Service http://web.mit.edu/facilities/transportation/shuttles/index.html :  
"The Parking and Transportation Office can also provide charter shuttle  
services to MIT departments on weekdays. Please call 617-258-6510 or  
email mitparking@mit.edu for more information."

Peter Pan Bus Services is currently the preferred charter bus company 
with MIT.  See  Peter Pan Bus Service
for more info.  BostonCoach is also an MIT partner vendor and I think they do charter  
buses as well.  See  Boston Coach for more info.

Also, Uber is available for alternative to taxis.