I've just finished building this multi-user, sequential/order sensitive and programmable combination lock. It is the best combo lock I've ever built, and it's probably one of the most efficient and secure ever.
It is 100% secure thanks to a complex circuit that I've invented (or that, at least, has never been published on YouTube).
Currently, it has 4 users and the passwords have 4 digits. Every user has a different password, and if password and user don't match, the door won't open. Also, if you press more than one user the door won't open.

DOWNLOAD ZIP FILE: http://www.mediafire.com/?x0t85odxxjrmk8h
DOWNLOAD RAR FILE: http://www.mediafire.com/?6kijepbn34fusvp

YOUTUBE SHOWCASE: http://youtu.be/M-HSfRk4FSQ

For all of those still interested, I'll keep working on it and making it more compact :)
This is just a showcase to show how it works, as you can see there are huge gaps between every circuit which could obviously be removed :)