Simply put, they are a company that buys a ton of stuff in bulk, then sells it at a discounted price. Typically they sell the kind of junk you probably don't need, but they price it so low that you kind of have to buy it. Every night at 11:00 CST a new sale is launched. These items are only available for 24 hours, or until they sell out, whichever comes first. If something is selling too quickly in the morning, they will pause the sale until 7:00AM CST to give the whiners people who sleep at night a chance to buy it. A special limited stock of items is also reserved for a sale at 03:00PM CST for VMP members. If you don't know what that is, it doesn't matter, because it's going away for new subscribers.
Meh Stalker was created by woot user Lichme (the same guy who created Woot Stalker. It is a page that can save you a lot of time trying to find the stuff you are looking for.
The main feature is a searchable history that shows previous sales and videos, however it also displays sales from their partner site MorningSave, which features more of the same types of items, grouped in limited time sales.
A fuku is a magical mystery sale, and the contents of it are unknown until you get it. Why would you want it? Because it's exciting, it's cheap, and it's fun. Many users will try to get one, however only a few will succeed. Meh Stalker isn't really useful for helping you buy one though.