It's the massachusetts bay transportation authority that we all know and hate and love. I'm trying the ride the whole thing like 2 or 3 routes at a time, just to say I did (and maybe learn some stuff along the way, and get better at writing). I am not the first (or second or third probably) to do this; my main inspiration is Miles Taylor↗, though I plan to format my posts differently than his or others' who have taken this quest.
The requirements for me to complete a route:

• I need to ride the whole route (for bus routes I can get on or off close enough to the end even if it's not the actual end)
• The whole route means the typical route for whatever day I'm riding on (for buses, small detours are permissible)
• The whole needs to using the vehicles it typically uses (so I can't ride a train line that's temporarily replaced with buses)
• If the route is more frequent than every 20 mins, I need to ride both ways
• My whole ride must be during daytime

It may look like I haven't even started riding yet, but I have - I just haven't started writing yet.

There are (essentially) (debatably) five rapid transit lines in Boston going up to 10.7 miles away from the square that they form downtown where they all meet. I'm obviously riding all 5 (questionably defined) lines... eventually... once they start working properly...
2/5 completed, 0/5 written up

• Green Line (all the branches!)
• Red Line (both branches and also the Ashmont-Mattapan High Speed Line)
• Orange Line
• Blue Line
• Silver Line (Yes, I am considering it rapid transit for this purpose. Yes, even 4 and 5)

A lot of routes, and many of them not frequent, and subject to change in a few years. I'm doing these mostly in groups of about 3 at a time, so there will actually be fewer than 146 write-ups.
30/146 completed, 0/146 written up

• CT2 Limited Sullivan - Ruggles
• CT3 Limited Beth Israel Deaconess Hospital - Andrew
• 1 Harvard - Nubian
• 4 North Station - Tide St
• 7 City Point - Otis & Summer
• 8 Harbor Point - Kenmore
• 9 City Point - Copley
• 10 City Point - Copley via South Bay Ctr
• 11 City Point - Chauncy & Summer
• 14 Roslindale Sq - Heath St
• 15 Fields Corner - Ruggles
• 16 Forest Hills - Andrew
• 17 Fields Corner - Andrew
• 18 Ashmont - Andrew
• 19 Fields Corner - Kenmore
• 21 Ashmont - Forest Hills
• 22 Ashmont - Ruggles via Talbot Ave
• 23 Ashmont - Ruggles via Washington St
• 24 Wakefield & Truman - Ashmont
• 26 Ashmont - Norfolk St Loop
• 28 Mattapan - Ruggles
• 29 Mattapan - Jackson Sq
• 30 Mattapan - Forest Hills via Cummins and Roslindale Sq
• 31 Mattapan - Forest Hills via Morton St
• 32 Wolcott - Forest Hills
• 33 River & Milton - Mattapan
• 34 Dedham Sq - Forest Hills
• 34E East Walpole - Forest Hills
• 35 Dedham Mall - Forest Hills
• 36 West Roxbury VA - Forest Hills
• 37 Baker & Vermont - Forest Hills
• 38 Wren St - Forest Hills
• 39 Forest Hills - Back Bay
• 40 Georgetowne - Forest Hills
• 41 Centre & Eliot - JFK/UMass
• 42 Forest Hills - Nubian
• 43 Ruggles - Park St
• 44 Jackson Sq - Ruggles
• 45 Franklin Park - Ruggles
• 47 Central Sq Cambridge - Broadway
• 50 Cleary Sq - Forest Hills
• 51 Reservoir - Forest Hills
• 52 Dedham Mall - Watertown Yard
• 55 Fenway - Copley
• 57 Watertown Yard - Kenmore
• 59 Needham Junction - Watertown Sq
• 60 Chestnut Hill - Kenmore
• 61 North Waltham - Waltham Center
• 62 Bedford VA - Alewife
• 62/76 Bedford VA - Alewife via Hanscom
• 64 Oak Sq - Kendall/MIT
• 65 Brighton Center - Kenmore
• 66 Harvard - Nubian via Allston
• 67 Turkey Hill - Alewife
• 68 Harvard - Kendall/MIT
• 69 Harvard - Lechmere
• 70 Market Place Dr - University Park
• 71 Watertown Sq - Harvard
• 73 Waverly - Harvard
• 74 Belmont Center - Harvard via Concord Ave
• 75 Belmont Center - Harvard via Huron Ave
• 76 Lincoln Lab - Alewife
• 77 Arlington Heights - Harvard
• 78 Arlmont Village - Harvard
• 80 Arlington Center - Lechmere
• 83 Rindge Ave - Central Sq Cambridge
• 85 Spring Hill - Kendall/MIT
• 86 Sullivan - Reservoir
• 87 Arlington Center - Lechmere
• 88 Clarendon Hill - Lechmere
• 89 Davis - Sullivan
• 89 Davis - Assembly
• 91 Sullivan - Central Sq Cambridge
• 92 Sullivan - Downtown via Main St
• 93 Sullivan - Downtown via Bunker Hill St
• 94 Medford Sq - Davis
• 95 West Medford - Sullivan
• 96 Medford Sq - Harvard
• 97 Malden Center - Wellington
• 99 Woodland Rd - Wellington
• 100 Elm St - Wellington
• 101 Malden Center - Sullivan via Winter Hill
• 104 Malden Center - Sullivan Ferry St
• 105 Malden Center - Sullivan via Newland St Housing
• 106 Lebanon Loop - Wellington
• 108 Linden - Wellington
• 109 Linden - Sullivan
• 110 Wonderland - Wellington
• 111 Woodlawn - Haymarket
• 112 Wellington - Wood Island
• 114 Market Basket - Maverick
• 116 Wonderland - Maverick via Revere St
• 117 Wonderland - Maverick via Beach St
• 119 Northgate - Beachmont
• 120 Orient Heights - Jeffries Point
• 121 Wood Island - Maverick
• 131 Melrose Highlands - Malden Center
• 132 Redstone - Malden Center
• 134 North Woburn - Wellington
• 137 Reading Depot - Malden Center
• 171 Airport - Nubian
• 201 Fields Corner Loop via Neponset Ave
• 202 Fields Corner Loop via Adams St
• 210 Quincy Center - Fields Corner
• 211 Quincy Center - Squantum
• 215 Quincy Center - Ashmont via West Quincy
• 216 Houghs Neck - Quincy Center via Germantown
• 217 Quincy Center - Ashmont via Wollaston
• 220 Hingham Depot - Quincy Center
• 222 East Weymouth - Quincy Center
• 225 Weymouth Landing - Quincy Center
• 226 Columbian Sq - Braintree
• 230 Montello - Quincy Center
• 236 South Shore Plaza - Quincy Center
• 238 Holbrook/Randolph - Quincy Center
• 240 Avon Sq - Ashmont
• 245 Quincy Center - Mattapan
• 350 North Burlington - Alewife
• 351 Bedford Woods Dr - Third Ave
• 354 Express North Burlington - State
• 411 Jack Satter House - Malden Center
• 424 Eastern & Essex - Wonderland
• 426 Express Central Sq Lynn - Haymarket
• 428 Express Oaklandvale - Haymarket
• 429 Northgate - Central Sq Lynn
• 430 Saugus Center - Malden Center
• 435 Liberty Tree Mall - Central Sq Lynn via Peabody Sq
• 436 Liberty Tree Mall - Central Sq Lynn via Goodwin Circle
• 439 Nahant - Wonderland
• 441 Marblehead - Wonderland via Paradise Rd
• 442 Marblehead - Wonderland via Humphrey St
• 450 Express Salem Depot - Haymarket
• 451 North Beverly - Salem Depot
• 455 Salem Depot - Wonderland
• 456 Salem Depot - Central Sq Lynn
• 501 Express Brighton Center - Federal & Franklin
• 504 Express Watertown Yard - Federal & Franklin
• 505 Express Waltham Center - Federal & Franklin
• 553 Roberts - Newton Corner
• 554 Waverly - Newton Corner
• 556 Waltham Highlands - Newton Corner
• 558 Riverside - Newton Corner
• 712 Contracted Point Shirley - Orient Heights via Revere St
• 713 Contracted Point Shirley - Orient Heights via Winthrop Center
• 714 Contracted Pemberton Point - Station St Hingham
• 716 Contracted Cobbs Corner - Mattapan

For now, the Commuter Rail is actually 2 separate networks, with no good link between North and South stations. For now, frequencies are a sad every 2 hours a good chunk of the time. For now, it runs with diesel locomotives, even on an electrified line. I'll probably be finished riding before they even fix one of those things.
0/16 completed, 0/16 written up

• Fairmount Line
• Fitchburg Line
• Foxboro Line (if they're still running regular non-event service when I get to it)
• Franklin Line
• Greenbush Line
• Haverhill Line
• Kingston Line
• Lowell Line
• Middleborough/Lakeville Line
• Needham Line
• Newburyport Line
• Providence Line
• Rockport Line
• Stoughton Line
• Worcester Line
• CapeFlyer (seasonal service) (does that count?)

Fun boats and water and stuff
2/5 completed, 0/5 written up

• Charlestown Ferry
• East Boston Ferry (seasonal)
• Hingham/Hull Ferries
• Winthrop Ferry (seasonal)
• Lynn Ferry (seasonal)