I just finished a cross-country drive to Philadelphia, and brought back another plant from my mother's garden. It looks like a sedum, had flowers like a sedum, and grows like a sedum. It also has whorled leaves in threes just like the neon stonecrop that I brought back 29 years ago (Good job Mom!)

So what is this?

Looks like Sedum sarmentosum, a ground cover sedum. It can spread fast!
Stringy Stonecrop (Sedum sarmentosum)