Am I reading that correctly? For $50 you get ~1,000 transistors worth of die space, and it comes in a package? Are there any other limitations? Full-custom analog design if you wanted?
That's correct, although it's $100: $50 for the space on the group-run chip and $50 for the physical stuff: the chip and the dev kit.
> Are there any other limitations?
Yes. Although, fewer and fewer with each next iteration.
> Full-custom analog design if you wanted?
For analog design, you would need to deal with https://efabless.com/ directly, pay $10k and get 100 QFN chips back with your design some time later.
TinyTapeout is digital-only, for now.
Sources:
2. https://docs.google.com/document/d/1sMmoCfS5l6Uz8sl9Bk3R32Xt...
It's also unsuitable if you want to keep your design private. Basically, the way this works is that all the different designs are placed on a single chip, with address pins to connect your design to the io pins. This means that everyone participating will have access to all functionality. You essentially buy a single tile in a shared chip.
This is also why it can be done so cheaply. Making 500 copies of 1 chip is way easier than 1 copy each of 500 different chips.