Milestone
I've been working on a particular project at work for somewhere around a year now*. During that time I've done the detailed design for and implementation of two closely related components of it and, more recently, integration of them with other people's work.
The integration part worked under UNIX late last week, and almost worked under Windows too - the thing that was holding it up turning out to be a bug in a low-level library which must have been there since it was written, but has never seriously affected anyone before (you have to use it in a very specific way to trigger it and some of the details haven't been possible to achieve until recently). That's now fixed.
Other bits don't work, but they are outside of my domain for the time being; and bugs remain in my code, but the known ones are inconvenient rather than serious (and several got fixed today). Seeing it start up on a Windows box today represents a significant milestone for me, and having got to that stage is a huge relief.
(We're only releasing under Windows for the first version, but I do almost all the development work under Linux - I'm much more familiar with the tools. A big chunk of the software runs in a POSIX-like embedded environment in any case.)
* In fact, one of my colleagues says that as of today he's been here for a year, and I was fairly well stuck in when he started, so more than a year rather than less.