Useful Programs

Small Text Generator - Generates small text font.
Adventure Converter - Helps to convert legacy chat colors to MiniMessage formatting.
SimplyMC - Contains a gradient generator, spark anaylzer, timings anaylzer and more.
Rainbow Text - Generates rainbow text useful for alternating colors.
MC-Tools - Votifier Tester, MoTD generator and some other misc tools.
Font Converter - Another small text font converter.
Startup Flags - Automatic optimized startup flag generator.
Centered Text Utility - Automatically centers any text inputted.
Disk.gg - Gradient generator, text centering utility, & rainbow text generator.
World Size Calculator - Useful for figuring out how much space your world will take.

Performance Guides

Performance Guide - Useful starter optimization guide. [YouHaveTrouble]
Another Performance Guide - Useful optimization guide. [Eternity]
Premade Configurations - Some premade configurations personally unsure how well these work.
Client Optimization Guide - Guide on how to optimize your minecraft client.

List of Shame - List of shame by a core paper developer
List of Fame - Some interesting projects in the minecraft community
Madeline Miller's Blog - Blog by one of the worldedit developers
New Common Exploits and How to Fix Them - A useful gide on fixing common exploits.