The most common source of bugs and system malfunctions are deployments of new software and changes to configuration of existing systems. So, whenever a problem arises my first question is always "what has changed"? With just a few programmers and a simple system, it's not so difficult to keep all changes in one's head, but with more people and more complex system tracking of changes become more important. At Zemanta, we don't have any proper tracking of deployments and configuration changes at the moment. The best what we do is to send a release email upon deployment. But searching inbox for release emails upon debugging isn't the most efficient way and we aren't consistent with writing release emails anyway. I would prefer a software or service that supports posting of new change entries manually and through an API for automatic deployment procedures. Additionally it should provide a timeline of changes, grouping of entries by projects and decent search.
Big shots such us Facebook and Etsy rolled their own systems for tracking system changes, but I would prefer a ready made solution that we don't need to support internally. I wasn't successful at finding such software or service, so I'd like to ask you for help and to share your experience in the comments.