My boss posed this problem to me:

• Encrypted: We need an encrypted database for miscellanious passwords we use at work that are currently only in people's head.
• Easily accessable: Someone needs to be able to quickly access specific passwords, possibly at hectic moments. This requires any sort of public key management (keeping it on a USB key in a sealed envelope?) to be relatively easy.
• Access control: The system should have groups of passwords where only specific people have access to specific groups.
• Recoverability: We need to make sure passwords from one group aren't lost even if the only users with direct access quit or pass away—hence we need some way where (for example) any two members of senior management may override the system (see the treshold link below) and retrieve all the passwords with their key.

The first thing that jumped into my mind was some form of threshold and asymmetric cryptography but I don't want to reinvent the wheel, are there any solutions for this?

Any software should preferrably be free and open-source.