Finding a list of all double-underscore variables?

Question

Related: What is the common header format of Python files?

Where can I find a list of all double-underscore variables/keywords that are commonly used in Python?

In Python, variables starting and ending with double underscores are typically to store metadata or are built into the system. For example,

#!/usr/bin/env python

__author__ = 'Michael0x2a'
__license__ = 'GPL'

class Test(object):
    def __init__(self):
        print 'Hello World!'

if __name__ == '__main__':
    t = Test()

I'm pretty certain __author__ and __license__ are pretty well known. What other double-underscore metadata variables are there? Is there a comprehensive list I can check somewhere? Can I just make up my own, or are there a bunch of ones that have become de-facto standards that I should use?

Things like __init__, __name__, and __doc__ are pretty much built into Python. Are those the only two reserved double-underscore keywords? Are there any more? Is there some place I can get a list?

[Edit]
I was browsing and encountered another question that linked to a mindmap of a bunch of double-underscore variables.