Semiphemeral protects your privacy by making it easy for you to automatically delete years of old tweets while giving you control over exactly which tweets you want to make sure you keep.
For example, you can set it to automatically delete tweets that are older than 30 days unless they have at least 20 retweets or at least 20 likes (all these numbers are configurable). You can also:

Keep all tweets that are part of the same thread as a tweet that meets those RT and like thresholds

Search through all of your tweets and pick which ones to exclude from automatic deletion, so that Semiphemeral will never delete them

Unretweet tweets after a number of days

Unlike tweets after a number of days

Automatically delete your old direct messages

Delete old tweets.

Forget is a service that automatically deletes your old posts that everyone has forgotten about. Shouldn't databases forget too?

Forget is a service that automatically deletes your old posts once everyone has forgotten about them. After all, why shouldn't computers forget too?