Quoting from Cydget's description in Cydia:

Cydget is a flexible and powerful replacement system for WinterBoard Lock Widgets, allowing users to have multiple lockscreen displays active and to cycle between them. Developers and web designers can make "cydgets" using either native code or HTML with JavaScript and Cycript (a JavaScript superset that allows flexible access to Objective-C).

Cydget is built on Apple's "SpringBoard plugin" mechanism, so it does not conflict with other Apple-provided lockscreens, including VoiceRecorder and Nike+. However, some jailbreak lockscreen extensions are not compatible with Cydget, which may cause humorously overlapping displays if you have multiple lockscreen extensions active at the same time.