Nestwork.net provides a painless way to backup and track changes to your Twitter Nestwork.  Backups are generated every few days and either emailed to you automatically or kept available for download at your leisure.  

Each backup will contain your nestwork of friends, followers and lists in a format that is both human readable and machine readable. This backup can be used to recreate* your Twitter account should it be banned or reset.

Curious who is not following you any longer?  Worried about the impact the Twitter Unfollow Bug is having on your account?  We track your nestwork over time and can show you statistics and details about how your “nestwork” has changed both intentionally and unintentionally.

*Via the API, the friends list can be rebuilt automatically.  There is not a way to re-add followers, but it should be possible to send tweets to former followers so they can follow you once again.