There are a number of tools which we have found useful to aid ourselves playing Pokemon. These are documented below.
A list of all current events and when they finish can be found on https://www.p337.info/pokemongo/
The Silph Road Atlas allow submitting of nesting Pokemon. https://thesilphroad.com/atlas
To find the specific IV of Pokemon you can use an IV checker.
For iOS devices we recommend using Poke Genie.
Calcy IV can determine the amount of Gym progress to the next level.
Both Calcy IV and Poke Genie offer Raid Simulators which will base the data on your scanned Pokemon.
A website that runs more accurate raid simulations is Pokebattler. This performs Monte Carlo simulation to roughly estimate the number of people needed to take down a raid based either on general levels or your specific Pokemon.
Breakpoints are levels at which a Pokemon's fast move will do one extra damage when fighting another Pokemon. These breakpoints are important as a Pokemon's strength will greatly increase after reaching it. Breakpoints can be found on dominikzen.
PVPoke is an open-source tool for simulating, ranking, and building teams for Pokemon GO PvP (player versus player) battles.
The Gym Badge Progress checker allows you to see the progress of gym your gym badges by uploading a screenshot.