Mark Allen

This is a filter for the FeedWordPress plugin. If you don’t use FeedWordPress this plugin will not be useful to you.
I wrote this filter after seeing the same post in my database 32 times. Maybe you’ve had the same problem, and I hope this filter helps you solve it.
The filter works by hooking the “syndicated_post” action of FeedWordPress and the “save_post” action in the core of WordPress.
For each potential post from a feed, the plugin attempts to find an identical SHA1 hash of the first 1024 non-whitespace characters (stripped of HTML tags) of the post content. 
If it finds a match the post is skipped. If not, the post is processed and a hash is inserted into the post’s metadata. (Stored as key _dpf.)
NOTE: No filter is going to be 100% accurate. This filter will stop most or some duplicates, but in all likelihood, will not stop all of them. 
If you want a filter that stops all duplicates, this isn’t your solution. In my test installation I had 5 posted duplicates out of 
125 syndicated posts (4% false negative) out of a corpus of about 300 duplicates. Most of those false negatives were due to slightly different HTML markup 
in the post content itself. So my approach isn’t perfect, but it is “good enough” for me.
<h3>Important Note</h3>
This filter can only check future syndication posts. Whatever duplicates are already present in your WordPress installation you’ll have to remove/clean-up on your own.
<h3>License</h3>
Copyright (C) 2012 by Mark R. Allen 
All rights reserved.
Redistribution and use in source and binary forms, with or without modification, are permitted provided that the following conditions are met:
<ul>
<li>Redistributions of source code must retain the above copyright notice, this list of conditions and the following disclaimer.</li>
<li>Redistributions in binary form must reproduce the above copyright notice, this list of conditions and the following disclaimer in the documentation and/or other materials provided with the distribution.</li>
<li>Neither the name of Mark Allen nor the names of any contributors may be used to endorse or promote products derived from this software without specific prior written permission.</li>
</ul>

FeedWordPress Duplicate Post Filter

A FeedWordPress syndicated post filter that checks for duplicates before posting items from your feeds.

Adadaa

This is a plugin for the FeedWordPress.
You can do complicated keyword filters using AND, OR, and NOT logics. Plugin will look for user entered keywords in post_title, and post_content
<h3>Usage</h3>
It is not disabled out of the box and you should add keywords by clicking the Add a new keyword filter. You can add as many keyword filters as you want using one or all of the logics [OR, AND, or NOT]
You can add keywords for individual feeds as well. When you select Posts under individual feeds on the Syndication menu of FeedWordPress, you’ll have the same options to add keywords.
<ul>
<li>
Keywords are not case sensitive. Enter comma seperated list of words along with your selection of logics.
</li>
<li>
Do not leave extra space between words – unless you want it. The exact spacing will be matched.
</li>
</ul>

Ada FeedWordPress Keyword Filters

Filters posts syndicated through FeedWordPress by keywords.

FeedWordPress Duplicate Post Filter vs Ada FeedWordPress Keyword Filters