There’s a surprising amount of misinformation out there about whether software companies own the work that a programmer does in their spare time.
From my answer to the question on answers.onstartups.com:
Being an employee of a high tech company whose product is intellectual means that you have decided that you want to sell your intellectual output.
Read the whole thing here:
If I'm working at a company, do they have intellectual property rights to the stuff I do in my spare time?
You’re reading Joel on Software, stuffed with years and years of completely raving mad articles about software development, managing software teams, designing user interfaces, running successful software companies, and rubber duckies.