Well it looks like a marrow, which are a type of squash, particularly if the fruits resembled courgettes (or zucchini, depending where you live) when they were small. On the other hand, there are green varieties of butternut type squash, such as Barbara and Zucca di Milano, but Barbara usually has yellowish stripes or mottles. If you planted a bit later than you should, they may still be butternut squash which just haven't changed colour yet, hard to say.
Not sure what you mean by 'how to process them...' do you mean how to prepare and cook them? If you do, some ideas in the link below
http://www.thekitchn.com/12-ways-to-make-the-most-out-of-zucchini-and-summer-squash-recipes-from-the-kitchn-205318
UPDATED ANSWER
Ah, well, there's your answer then - your saved seed was a result of cross pollination of your plants last year, and that means you've got squash this year, but who knows quite what type of squash, they don't come true from seed. Bear in mind that a squash is a squash - whether its a pumpkin or butternut or marrow, the only query with yours is, are they ripe...and what will they taste like...