Fastpass+

FastPass+ Availability:

The Dibb's Fastpass Availability post - updated daily, shows availability for groups of 2 and 4 for up to 90 days in the future for several of the most popular attractions. Use this resource when preparing to make reservations at the 60-day mark, will give you a good idea of what will not be available at 60, 61, 62, 63 days.

touringplans Fastpass Availability - only searches for groups of 1, but shows specific available times for every attraction. Updated every few hours for same-day fastpasses; useful for generally getting an idea of when same-day fastpasses run out, but not particularly useful for actually making reservations. Updated daily for future days up to 70 days in the future.

FastPass+ Finders:
(N.B. - I cannot vouch for the effectiveness or the safety of any of these. The latter two apparently require your MDE username and password)

fp4me.com - service that searches for specific fastpasses at specific times and sends notifications, but closed to new users (last checked 8/27/2019). No idea about how long the waitlist is or even whether new users are ever accepted off the waitlist. 

Disney-Fastpass-Bot - create your own app to search for fastpasses. For Windows 10, includes instructions for people with no programming experience. on GitHub from ethanbrimhall. 

Controlled Chaos Fastpass+ Finder - Easy-to-install app for Windows.