How does these work anyway?

Ok, I've seen greeting cards with those music, and those Tetris Handheld game which is sold at 99¢ in a cheap bargain shop.

All of them are similar - one black blob with some squarish thing in the center. Maybe it's a die.

What's in it anway? Mask ROM? Programmable Logic Device? Microcontroller?

And do they program those like in µC and then place them in the product afterwards?

It's a burning question, since I can't find the answer in the net. Enlighten me.

It's called COB (Chip On Board), it's most probably a mask programmed microcontroller, although various chips are available like that.