Currently I am using ATmel ATmega328's for all sorts of things (no Arduino, btw). They're either connected to an ENC28J60 from Microchip (ethernet mac&phy) or ESP8266. I love the ATmel microcontrollers, especially the ATmega's, because they have rich hardware functionality, they're cheap, they're in DIP-package (so you can solder them yourself) and most of all, documentation is excellent.
I now have some ESP-201's that have most of the pins available and I wonder if I could use some of them on their own, without the ATmega328. This would only be possible for situations were little I/O is required, as it appears the ESP8266 doesn't have that much free pins and also hardware peripheral implementations seem to be limited compared to the ATmega328.
So I am trying to get an overview what's possible and what's not, compared to a "regular" microcontroller. I think I already have quite a bit of information, please extend!