I think it's a common experience for software developers to have some abandoned, failed, outdated or otherwise discontinued projects somewhere on your disk. I also think that it's okay to start projects and to not finish them – sometimes the purpose of a project is to learn something new, waste time or pretend to be busy.
Given my assessment of the situation is correct, there must be a huge amount of code existing in the depths of our filesystems that a) doesn't attract us anymore b) may be interesting for others to see and maybe work on.
So what's the donate a project day? A simple idea: We figure out a certain date ( say, March 31 ). At that date, every participant publishes one of his or her abandoned projects at github or bitbucket. The second condition is that each participant must write something about the project, i.e. the motivation for starting it and some of the reasons that made him abandon it.
For the day to work great, we should have a page where all donated projects are collected and presented, as well as the common agreement that an open source license should be used for the published code, so others can continue where you stopped.
What's important isn't that your code is super-polished, perfectly documented or completely covered by tests, but rather that you just share it with others.
This is just a rough idea. What do you think?