MahTweets is a free, open-source, extensible Twitter + Facebook (& more) client for Windows. The MahTweets application was developed to be a small tool that provides support for Twitter and Facebook.

MahTweets Features:
1. Connect with Twitter, Facebook, Identi.ca, Yammer, Plurk & 12seconds
2. Upload to Flickr, Twitpic, Twitgoo, Twitrpix, YFrog
3. Powerful filtering
4. Geo-tagging support (both viewing geotags and sending)
5. Twitter lists
6. Auto-splits tweets over 140 characters
7. Real time search

1. Awesome media handling
It's a pain having to go out of your twitter client just to view a picture on twitpic, particularly when somebody is just posting what they're eating for breakfast. MahTweets lets you view pictures from twitpic, flickr or absolute urls inside the client.

2. Auto-expand shortened urls
Tired of being Rick Rolled (I'm looking at you @griffmiester) through tinyurl, is.gd, bit.ly (and many others)?

3. Filtering/Grouping
MahTweets has some of the most advanced and customisable filtering & grouping of any Social Media client.

4. Autocomplete everywhere
MahTweets has inline replies, as well as the main 'composition textbox' at the top - and throughout all plugins, all places you can enter in an update, Auto-complete is enabled

5. Real time search
MahTweets 2.7 enables the full Twitter Gardenhose for realtime searching - you get search results as soon as they are tweeted!

The real power of MahTweets is hidden away in plugins.

MahTweets makes use of the upcoming .NET 4.0 feature, Managed Extensibility Framework, to create a robust, extensible social network client.

The full list of official plugins is:
1. Twitter
2. Facebook
3. Plurk
4. Identi.ca/StatusNet
5. Yammer
6. Ping.fm
7. RSS Feeds
8. 12seconds
9. YFrog
10. Twitpic
11. Twitgoo
12. Twitrpix
13. Flickr
14. Tinyurl
15. is.gd
16. Tr.im
17. Bit.ly
18. Logitech G15/G19 display

Requirements
* Windows XP/Vista/7 (32bit or 64bit)
* .NET 3.5 Service Pack 1

The license of this software is Freeware, you can free download and free use this social networking software.