The Archivist, a Windows application from MIX online Labs runs on your local system and allows you to archive tweets for later data-mining and analysis for a given search. The Archivist allows you to start a search and will get as many results as it can on the initial search. If you leave The Archivist open, it will update with the latest results every 10 minutes. You can also close The Archivist and open it later. The Archivist will save the tweets and get all the tweets it can since that search.
The Archivist will display a chart that shows the number of tweets per day for a given search, so that you can quickly assess traffic for a given search.
The key aspect to The Archivist is using Twitter Search. To learn more about creating Twitter Searches, read their documentation on search operators.
The Archivist was used for digging up, analyzing some interesting stats during MIX10.
For more details , system requirements and installing The Archivist, please check - http://www.flotzam.com/archivist/