What Will Happen to Zimbra? (Groklaw)

In some proprietary software contracts, the customer inserts a clause on 'change of control'
meaning that when the software vendor is taken over (or in some cases even if their software
is no longer competitive generally), the source code is automatically released.  A very common
contract item is that if the vendor goes bust their source code is released.  This is done
through 'source code escrow' in which a trusted third party is given snapshots of code by the
vendor whenever there is a new release, and the third party has strict rules based on contract
as to when it can release the software to the customer.

The NCC is a UK organisation that does a lot of this, and has a useful set of guides - see
http://www.ncc.co.uk/research/projects/escrow_guide.cfm - and there's also a short Wikipedia
article at http://en.wikipedia.org/wiki/Source_code_escrow. There are many commercial
providers of source code escrow.