ScratchJS - An extension with over 240 blocks!
I've been making a block extension called ScratchJS, and it adds over 240 different blocks to the editor!
Some of the categories:

• JSON
  
• JavaScript
  
• Input
  
• Local Storage
  
• Temporary Variables
  

And a lot more (we have over 20 categories)! We also have blocks that extend the existing categories of Scratch.
One of the most useful blocks we have is this block:

Get return value of [JavaScript code here]::reporter #FF6600

It runs the JavaScript code within and returns the value. Some other blocks include:

when <ARRAY | Array (Get all pressed keys::#FF6600) contains [e]::#FF6600> is true::hat #FF6600
Set temporary [myTemporaryVariable] to [something]::#FF6600
Show alert (Get temporary [myTemporaryVariable]::#FF6600)::#FF6600

We're looking for developers to help us add blocks and fix bugs! If you're interested, go to our GitHub repo.
We also have a website here.
You can get the bookmarklet that adds the extension to your project at either the above website or on this project.
We're also looking for block ideas! Feel free to post an idea below.