VisBio development has ceased in favor of ImageJ2. Our eventual plan is to integrate VisBio's unique functionality into ImageJ as a VisBio plugin suite.
Historically, we released new versions when a significant number of bugs were fixed, or when significant new features were added. Take a look at the What's New sidebar on the VisBio home page to see the release history. To be notified of any future releases, sign up for the LOCI software mailing list.