Some of my favorite answers:

Networking:

• Should checksum be added to custom network protocols?
• Why use TCP and not UDP if you have your own error detection?
• What is the effect of setting the priority of a Linux socket?

Java & Multi-threading:

• Java Memory Model - Happens-before relationship with volatile fields
• What is the difference between Java Future, CompletableFuture and RxJava?
• How multi-threaded software scales with the number of threads
• How does the JVM generate the names of network interfaces on Windows?

Rosenberg’s Law: "Software is easy to make, except when you want it to do something new. And then, of course, there is a corollary: The only software that's worth making is software that does something new."