In 1637 New England, John Harvard could have used his donation of 779£ 17s and 2d to buy 26,738 pounds of butter.

I'm not generally one for "currency equivalents" across centuries and space, since that doesn't really tell us anything about either purchasing power or purchasing needs in a given historical context. Fortunately, in this case we have some more useful data to judge against--yes, even more useful than the 46,791.5 pounds of bacon his descendants could have bought in 1653.

Massachusetts Bay Colony was founded to be a Puritan "city on a hill" and the future Harvard was to be its seminary. In 1636, its governing General Court thus authorized 400£ to go towards the establishment and construction of its seminary. Except there was one problem. Massachusetts Bay Colony didn't have 400£ to spare--that was actually a little more than they collected in taxes that year! The agreement, then, was to spend 200£ right away and 200£ once the school began operations (books, faculty, and so forth). Thus, John Harvard's donation either tripled or quintupled the money available to the nascent seminary.

And we shouldn't ignore the other half of his donation, either. A full library was one of the seminary's biggest priorities, too. In terms of other early donations, one of the most significant was a collected 200£ earmarked for further book purchases.

Books might not seem like a massive expensive compared to, say, a building (unless they're published by Brill...). But this is where the realities of a colonial economy come into play. In the strictest sense, the colony-metropole relationship is one in which the colony is a producer of commodities with a primary/privileged economic relationship to the metropole. America grew things; Britain made things. Here those things included books.

North America's first printing press was established by Elizabeth Harris Glover (later Dunsten) in 1638, too, and that was just one press. Until that point, all books in New England had to be bought or brought from overseas (I'm not sure if book printed from New Spain's presses ever made it north), and let's remember that a printing press can only be cost-effective in mass production. Printing two sets of Calvin's Institutes isn't going to support anyone's family. Almost a century later, Benjamin Franklin was still complaining that nearly all the texts printed locally were broadsheets and primers.

Furthermore, even with Glover and her printer Stephen Daye potentially hired to make more frequently referenced books for the seminary/college, replacement letter molds and all the paper still had to be shipped from England. At great cost, too--when her late husband Joseph made arrangements to bring his press to America from England, the Glovers actually brought more paper with them than their press itself was worth.

John Harvard could have done the things that rich people do with their money--buy nicer things than you have, not do the crummy chores that you have to do, and make more money. In fact, we know he did at least some of those, since his book collection was also quite significant. But in this case, he also played a big part in making the college eventually named after him happen.

Still, that much bacon...

I agree with /u/sunagainstgold that translating currencies across centuries isn't necessarily the most useful information but I do have a document which would make an inflation calculation possible. I used it as a source writing a paper about wage laws back in college but in its discussion of wages it talks quite a bit about what money could buy in a few colonies.

History of Wages in the United States From Colonial Times to 1928 courtesy of the US Department of Labor and its Bureau of Labor Statistics. In Section 1 Chapter 2 you'll find this this in reference to Massachusetts Bay Colony

Corn sold in 1631, the year in which it was made a legal tender, at 10s. ($2.43) to 11s. ($2.67) a bushel; the next year the price had fallen to 4s. 6d. ($1.00), recovering slightly, in 1633, to 6s. ($1.46) per bushel. Its selling price fluctuated between 4s. 6d. and 6s. until 1641, and its currency value as set by the [Massachusetts general] court varied accordingly.

So that converts 6 shillings to $1.46 in 1928 dollars right around the period we're looking at, since there are 20 shillings to a pound £779 would be 15,580 shillings. Divide that by six and multiply the result by 1.46 gives us $3,791 (and a fractional amount I'm going to round) in 1928 dollars. This can then be plugged into something else provided by the Bureau of Labor Statistics, their handy inflation calculator to give a final total, in 2017 dollars, of $54,653.36

Now that may not seem very impressive but it was quite a bit in terms of relative buying power and the library itself was a substantial gift but that's already been pretty well covered. If you're curious there are a number of charts so you could see how much corn or wheat could be bought rather than butter.

I found slightly more novel something to spend that money on in this little bit though,

To illustrate, Boston’s first lawyer undertook a case for a carpenter of Cambridge who received as part of his pay for the con­struction of a house “ one cowe and one steere calfe” valued, by the employer, at £25 ($121.50). According to the plaintiff, that price “ was then overvalued £5 [$24.30] at least.” The carpenter had to pay his workmen £9 ($43.75) in money for their work on the job. Later, when he tried to market his cattle, the price had fallen so that “ now they are not worth above £12 [$58.32].” In addition to the loss of £13 ($63.18) in the value of the stock, the plaintiff had been at an expense of “ £2 10s, [$12.15] for the keeping of them since, which amounts to £15 10s. [$75.33],” the amount entered in the petition for relief.

So if you were a carpenter in Cambridge at the time you could have used £779 to pay your workers to build about 86.5 houses. You also could have housed a steer and a calf for quite awhile but I'm unable to perform an actual calculation since the time period he housed them for wasn't actually specified.

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