Solar is similar to but distinct from these other PHP projects.
- Solar is also similar to Horde in that it attempts to provide a cohesive framework for application development. Horde has a long and distinguished history, but is based on PHP4; while this does not prevent Horde from being used in a PHP5 environment, it is not E_STRICT compliant.
- The Solar project is similar to PEAR in that it provides a class library of useful components for PHP development that adhere to a common standard of development. However, with the exception of the base PEAR classes themselves (e.g. PEAR_Error), classes in PEAR are not intended to be a cohesive framework.
- Solar and ZF look very similar at first glance; however, Solar pre-dates the Zend Framework by about a year. You can read more about the differences here.