I have no idea what species they are, but they aren't houseflies. They are about a quarter of an inch long, and their translucent wings look too small to carry their bodies. Maybe that's why they don't fly very well. I don't recall ever seeing them in earlier years. I poked around on teh Internets to see if I could find out what they are, but there are way too many species of small flying insects that appear in early autumn for me to search through them to find mine. Who knew?
For those of us not flies trapped in houses, the perfectly mild day was a pleasant opportunity to shed some clothing and do outdoor things such as rake leaves. So far there aren't so many leaves and I haven't dealt with them so frequently day after day that raking them becomes an onerous chore. In a month or so I'll be displeased by all the dead leaves needing to be raked, but now they are still a seasonal novelty. I made a nice little pile of them and let it be. No need to compost it yet. I like looking at it. Autumn, just sitting there.