Stardew Valley is a farming simulator similar to Harvest Moon on PC, that's currently waiting on a successful Steam Greenlight campaign. It'll feature online support for up to four people (drop-in and out), as well as full solo play capabilities.
Just like Harvest Moon, you'll have to manage resources as you grow your farm, in addition to leveling up your character with different skills like fishing and foraging.
I still remember the initial sense of wonder I had when playing the original Harvest Moon for the first time. Hopefully, Stardew Valley can recreate that.