Kohana is licensed under a BSD license, so you can legally use it for any kind of open source, commercial, or personal project.
Anything can be extended using the unique filesystem design, little or no configuration is necessary, error handling helps locate the source of errors quickly, and debugging and profiling provide insight into the application.
To help secure your applications, tools for input validation, signed cookies, form and HTML generators are all included. The database layer provides protection against SQL injection. Of course, all official code is carefully written and reviewed for security.
We are working very hard to provide complete documentation. To help improve the guide, please fork the userguide, make your changes, and send a pull request. If you are not familiar with Git, you can also submit a feature request (requires registration).
If you are having trouble finding an answer here, have a look through the unofficial wiki. Your answer may also be found by searching the forum or Stack Overflow followed by asking your question on either. Additionally, you can chat with the community of developers on the freenode #kohana IRC channel.