OnlineTools
A number of tools have been created for robot combat builders to be able to plan for and build effective bot weapons and drivetrains. Here are some community favorites:
Mechanical
Handy for drivetrains.
Belt Length Calculator - B&B Manufacturing
Belt Center Distance Calculator - Jeremy Germita
Chain Center Distance Calculator - Jeremy Germita
Motors
Electric Motor Math - Understanding the specs for PMDC (brushed) motors. By Team RoboForge, presented by Run Amok. Also see Deriving Motor Constants for surplus PMDC motors.
Motor Speed and Pushing Power - Choose brushed or brushless motors. By Jeremy Germita
Weapons
Use these to find out not only how hard a spinning weapon will hit, but also whether it is compliant with maximum energy rules for the events you compete in.
Spinner Weapon Kinetic Energy Calculator - SpinCalc by Run Amok. Read the help file! Mass, MOI, spin-up estimation, etc.
Tip Speed Calculator - Jeremy Germita
Tip Speed and KE (Kinetic Energy) Calculator - Bristol Bot Builders
Control
Mixer Fixer for correcting problems with channel mixing on your transmitter. By Run Amok.
for Event Organizers
Challonge.com - Well established web-based tool for competitive events and tournament brackets. Integrated ticketing and payment via Stripe. Features here.
TrueFinals.com - New site in beta for tournament brackets. Stats and dashboards, competitor list with next opponent listed, integrated check-in and call up, video overlays for match recording/streaming, all also web-based. Well-documented API and small robot combat community creating deep integration.
BigTimer.net - Large-display, ad supported, touch-enabled timer.