As I recall, one of the qualities of Twitter in the early days was a very open and accessible API that allowed a wealth of third party apps.
Many folks at the time, thought that this open API and the apps it allowed, was responsible for much of the early Twitter growth.
Then over time, as I understand it, Twitter slowly limited access to the API and cut off the growth of third party apps and built much of the functionality into Twitter itself.
@stpaultim @atomicpoet lots of sites had open APIs back in the day, they gave you free keys to do what you want. Of course, they still owned the doors, the locks, and the contents of everything inside...