2.0 networks are a series of blogs created in platforms like blogger.com, wordpress.com, tumblr.com... just to post some content and place links to money sites or any other intermediate to create some link juice and make them rank higher.

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Web 2.0 includes all of the social media websites. Think Facebook, Tumblr, Twitter etc. This can include wordpress, and blogger for their own platform sites.

Web 2.0 is all about interaction between the users on the sites.

Forums like this can be considered among the first web 2.0 properties.

Web 2.0's are sites which allow for user generated content

Some of the most popular web 2.0's currently include (not in any particular order) :

1) Youtube
2) Instagram
3) Imgur
4) Tumblr
5) Pinterest
6) Wordpress
7) Blogspot
8) Hubpages
9) Twitter
10) Slideshare

List Of Top Web 2.0's

Not unless you have the time or resources, more isn't necessarily better. Having a solid audience and user base on a handful of platforms is better than trying to spread yourself thin on all of them.

This is the difference

Web 1.0..........................-->...................... Web 2.0
DoubleClick.................... -->.......................Google AdSense
Ofoto..............................-->.......................Flickr
Akama........................... -->...................... BitTorrent
mp3.com.........................-->.......................Napster
Britannica Online..............-->..................... Wikipedia
personal websites.............-->....................blogging
evite..................................-->...................upcoming.org and EVDB
domain name speculation..-->.................... search engine optimization
page views........................-->....................cost per click
screen scraping.................-->...................web services
publishing........................ -->................... participation
content management systems...-->........... wikis
directories (taxonomy.........-->................. tagging ("folksonomy")
stickiness.........................-->................ syndication

Web 2.0 describes World Wide Web sites that emphasize user-generated content, usability, and interoperability. The term was popularized by Tim O'Reilly and Dale Dougherty at the O'Reilly Media Web 2.0 Conference in late 2004, though it was first coined by Darcy DiNucci in 1999.

That is the meaning found from google.

Here is the list of web 2.0 website are :
Top 100 Web 2.0 sites list 2015 ~ Blogger Tips and Tricks - Learn Creative Blogging Ideas Online

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Web 2.0 describes World Wide Web sites that emphasize user-generated content, usability, and interoperability. Web 2.0 Websites typically include some of the following features/techniques:

• Search: the ease of finding information through keyword searching.

• Links: guides to important pieces of information. The best pages are the most frequently
linked to.
• Authoring: the ability to create constantly updating content that is co-created by users. In
wikis, the content is iterative in the sense that the people undo and redo each other’s work.
In blogs, it is cumulative in that posts and comments of individuals are accumulated over
time.

• Tags: categorization of content by creating tags that are simple, one-word descriptions to
facilitate searching and avoid having to fit into rigid, pre-made categories.

• Extensions: automation of pattern matching for customization by using algorithms (i.e.
Amazon.com recommendations).

• Signals: the use of RSS (Real Simple Syndication) technology to create a subscription
model which notifies users of any content changes.

Generally Web 2.0 is for backlinking and content syndication

not sure why you think they are best for Page Authority or refer to in the old way Page Rank

From what I have found Page Authority is not as relevant as it has been in the past

Now it is all about Authority or what I like to use is Moz's Domain Authority since this is the only metric out there that even attempts to qualify what the difference is between websites for Authority

Google won't let us know so you use the next best thing out there is

Web 2.0 sites basically means hosted sites or blogs. Good guide here:

3 Minute Guide To Creating A web 2.0 Website | Boosites

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It's really good updates for web 2.0 .

Web 2.0 are the websites that emphasizes user generated contents. Some best web 2.0 sites are
Tumblr.com
wordpress.com
weebly.com
blogger.com
yolasite.com
soup.io
jimdo.com

Thanks for giving the information about 2.0 web site....

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web 2.0s sites are basically plays an important role to help your website rankings. Here are the top web 2.0s sites with good authority and page rank

free wordpress
weebly
tumblr
squiddo
hubspot
blogger
blogspot

Web 2.0 sites are help to drive the traffic and link Juice to your site. Here are some High PR Web2.0 site list

Web 2.0 is the best practice of content marketing. Its also an effective way of quality link building.

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Web 2.0 Submission is one of the best SEO activity which can easily share your content to increase the website traffic and increase keywords ranking. In present days every seo company using this technique to rank their client website in SERPs. Eg: Reddit, StumbleUpon, Delicious, hubpages, squidoo, blog sites.

Web 2.0 has been used more as a marketing term than a computer-science-based term. Blogs, wikis, and Web servicesare all seen as components of Web 2.0. Web 2.0 was previously used as a synonym for Semantic Web.Some of the best sites for submitting web 2.0 are
Blogger
wordpress
weebly
tumblr

Google love these sites. So if you have a website, try to get on these sites and link back to your main site.

Few of the web2.0 websites are Tumblr, Wordpress, Weebly, blogger, Blogspot, Jumla etc. These are high PR sites which allows to make web2 on it which is sames as a blog. These sites generate huge traffic by making quality backlinks using them.