at knownow i wrote an event-driven nonblocking http server in python with asyncore which could efficiently do comet over hundreds of concurrent http connections; existing http libraries were all blocking at the time
i also wrote a similar event-driven nonblocking http client in c for benchmarking and load-testing both that server and a different compatible one being written by another team in c++. this was nonblocking because it was important for the client to be faster than the server. at the time there was no libevent/libev/libuv so i wrote my own
at satellogic i maintained the upper layers of our cubesat space protocol stack, which provided a socket-like interface to our coap stack, which i also maintained part of
i also had to tweak kernel socket buffering settings for rabbitmq there
for wercam i'm experimenting with different approaches to ipc for efficiency; the data being transferred are pixel buffers so i don't think protobuf/thrift/etc. is going to help
for the mail server i share with some friends i wrote a milter in python to smtp-reject outside email to certain recipients unless it matched a whitelist; milter doesn't speak pb either and i couldn't find a python library
i wrote a multicast file transfer program in python (bccpo/bccpi) for copying files across the lan without having to fiddle around with ip addresses; the data being transferred is just (multicast) the ip and port and (unicast) the filename, file size, and file contents, so again i'm not sure pb would simplify anything. the hard part of getting it working was just multicast
i wrote a chat client for icb in python with asyncore, and again i couldn't find a suitable library
even when i'm using a library, it's often pretty useful to be able to read strace output or use select or poll with the file descriptor it's trying to hide from me
i don't think any of these qualify as either your category 1 or 2
i've also done a huge number of things that fall into category 2, of course, like writing an irc client in bash, writing a web server in assembly, and writing a chat server in three 80-column lines of c, writing a mud, and so on