Mysterious plant or weed

There is a plant that has cropped up in my front yard garden.  I don't recognize it nor could I find it in my plant books.  I have the University of Maryland's Master Gardener Handbook and checked the plant against the weed pictures and it wasn't there.  I think this is a weed but it could be something I planted last year and forgot about.  I'm hoping some of my garden pals will recognize it.  It seems to be spreading by runners - it's in quite a few places which leads me to think it's a weed.