A sweet friend of mine was asking what this fruit could be. She said it came off a large tree. She said the center is spongey with seed-like formations on either side of the center, also kind of soft. She said it smelled citrusy. Please excuse the out of focus pics.

Gee, my first thought was some type of Kiwi until I enlarged your photos
http://www.mofga.org/Publicati...

http://www.google.com/search?q...

I wonder if maybe it could be some type of Asian Pear, I think some are rather small in size.

or asian guava: https://robertishere.com/wp-co...

I'm not sure what hardiness zone Main is but I found this list of cold hardy fruit trees: http://www.30bananasaday.com/p...

What is the location where this fruit was found? Did anyone take a photo of the tree or leaves?

I've looked in some books and on the web and it would be easier if this was a tropical fruit as I found one or two similar, but unless your friend got it from a supermarket that's not likely in Maine

I wondered about pawpaw but didn't think it looked right inside although this picture of an unripe one looks closer:

https://travelingmarla.files.w...

She said there was no pit just the spongey center. It was on a large tree but she has not sent me a pic of the tree yet.

It does resemble the fruit of Pawpaw (Asimina triloba)