L2J is an alternate game server for Lineage2. The L2 protocol is reimplemented in the server, so you can play with this server without any modifications to the client (except changing the server IP address). The latest USA live client version is always supported, so don't expect this server to work with the PTS/Korean client.
WANsim allows you to simulate (more accurately, emulate) a WAN connection. In particular, it allows a user to change the emulated WAN speed, latency, variation, packet loss, packet duplication, and packet corruption aspects. It is configured as a network bridge that is established at boot time and uses the Linux Kernel NETEM functionality to accomplish its goals. Although relatively well documented, this functionality is not the easiest to use. WANsim wraps it into a simple to use script.