Just as promised, the PlayStation Suite software development kit has entered open beta. Sony is inviting interested developers to try making their own games and applications, test and debug their creations, and talk with other developers and Sony Computer Entertainment employees.
You can sign up on the official site. While the beta is free, you'll be required to sign a contract to continue using the tools once the full version launches, and you'll have to shell out $99 per year. That will happen some time later this year, but you can tinker for free for now. The closed beta has been running for months, but the open beta adds improvements based on feedback, and the ability to test content on the PlayStation Vita.
In a separate FAQ, Sony specifies that for your content to be sold on the PlayStation Store, you'll have to sign a separate contract. The ability to sell content will launch later this year alongside the full, paid version of the SDK.