Watermark is your personal Twitter app that runs in the cloud. It works in the background to store each tweet from everyone you're following, making your timeline fully searchable even when you're not using Twitter. Watermark remembers everything so you can find the tweets you care about.
There's nothing as powerful for archiving and search of Twitter and App.net. Watermark doesn't just keep your own tweets and favorites forever — it stores every tweet and App.net post from everyone you are following, so you can find what you need no matter who posted it.
Plus it's got advanced features like grouping tweets in named collections, saved filters that can be shared, and Dropbox sync for easy exporting.
“I use Watermark on a daily basis to retrieve tweets that have been shared in my timeline — status updates that would be hard to retrieve using Twitter’s web interface, let alone the official apps.” — Federico Viticci, MacStories