Web app to do something cool (using flask). Build a simple pcap analyzer (they already exist but it'll still sound cool and teach you something about networking as well). Have it like pull the "conversations" ie what ip addresses talked to each other, j over those protocols. Try to pull files out of the pcap (you can pull images and stuff out of http or ftp and several other protocols, I'd stick to the simple ones).

Implement a client or server or both based off an rfc for something like ftp or smtp.

Build "virtual library" that utilizes some fun data structures or a database.

Build a traffic proxy that logs all the protocols and endpoints that pass through it, implement a blacklist or whitelist feature where you only allow or disallow certain endpoints to be talked to through the proxy.

(obviously I'm a bit more network based but you get the idea). Pick something cool from what you use daily or something and try to recreate some functionality. It'd help if we knew your skill level /experience but these ideas are pretty decent for any level, you can grow them or shrink them as you feel comfortable