Open-source network emulators and simulators
The most important and most useful thing is the hardest to obtain: latency simulators.I just want an IPv4/IPv6 proxy that does nothing other than delay, rate-limit, and/or drop packets.This is a critical aspect of application performance that all developers just ignore because it's such a PITA to simulate.Your loopback adapter has a latency of 30 microseconds, but that same web-to-database connection might traverse multiple switches, routers, firewalls, and load balancers and have a latency of over 1,000 microseconds (1ms) in production. That's thirty times worse, and I'm not even talking about zone-redundant deployments, regional-to-region failover, or any such thing!Ditto with web apps, where every developer mistakenly believes that their Angular or React monstrosity is "performant"... because it is... on their own machine. With loopback networking. Try that over a 3G connection... in rural India. Not Indiana. India.