If you know about BeOS, you might also have heard of the Haiku project that aims to re-create BeOS in open source form, binary-compatible with its latest R5 release.
When Haiku decided to introduce package management, they choose a different but very interesting route: a virtual package filesystem.
In Haiku, packages are individual filesystem images that are mounted by the package system to create a filesystem. This has some advantages: Package installation is as simple as mounting them which happens instantly. All system files are read-only and therefor protected against unwanted changes (user error, malicious software). Changing to a previous system state is as simple as telling the package filesystem to mount a previous state, easily performed using the boot manager. User files or changes to the read-only system files can be made in a separate write-able part of the filesystem.
To better understand how it works, give Haiku a try. It runs amazingly fast in a virtual machine.
Some information about Haiku's package management:
Package Management - Present and (hopefully near) Future
Package Management, First Draft
Package Management for Haiku
All items tagged with package management