Viola labradorica

This is not an especially unusual plant, but anything that is blooming now in mid October has to be considered kind of special. Even more unusual to have a violet blooming this time of year.
Viola labradorica is also sometimes called Alpine Violet. The foliage is even tinted deep dusky violet. It is smaller than the usual wild violets and spreads by stolons sort of like a strawberry, which means that if you have one this year, you will have many next year. It also spreads by seeds. I have little colonies spread throughout the gardens and it never really would be considered invasive despite its tendencies to expand. Hardiness zones are zones 3 through 8.
Their main bloom season is in the spring, but they bloom here off and on all throughout the growing season. They will grow in sun to quite deep shade, though in the south, shade will be preferred. They prefer moist but well-drained soil. These violets will even tolerate a bit of light foot traffic, and given their diminutive size at only about 4 inches tall, they might be good between stepping stones, though I haven't tried using them in that way.
Labrador violets are native to the northern United States, eastern Canada and Greenland.
They are readily available from quite a number of mail order nurseries and aren't a bit expensive. I enjoy having them pop up here and there and should they ever get out of hand, they are very easy to thin out, unlike the other wild violets that we have here.
Jane