RSS Box generates the "missing" feeds for Twitter accounts, YouTube channels, Instagram users, and various other sites that fail to offer RSS.
This website lets you subscribe to RSS feeds for websites that do not support RSS themselves, by using the respective website's API and then translating that data to RSS feeds.
If you get a page saying "Application error", simply try again. This website resolves shortlink URLs to give the reader a better experience, and embeds linked content directly into the RSS feed. You will get this error if this takes longer than the web server allows.
Some websites, like YouTube, support RSS feeds but they are quite hard to find, so this website will provide the URL.