Paul Jones, lead developer of the Solar framework project has posted a few differences between his framework and the just released Zend Framework.

Even though (or perhaps because) the Solar project pre-dates the newly-released Zend Framework by about a year, I've had a couple of private emails asking me if I will discontinue Solar, or rewrite Solar on top of the Zend Framework. The short answer to both of these, at least for now, is "No - Solar is not going away." Especially now that I'm not at Zend any more.

He lists a few similarities first (based on general topics) but follows it quickly with some pretty significant differences between the two (with an emphasis on the "unified" nature of Solar vs Zend). Thrown in are also some other features that Solar has that Zend doesn't at this time - built-in localization, form processing, etc. Of course, there are some coming from the other perspective (that Zend has that Solar doesn't), though it's mostly things like "great marketing apparatus" and "a dozen regular individual and corporate developers and the backing of a real business" as well as lots specialty classes and more automated testing and documentation.

There's not any bitterness between the two frameworks, though, and Paul reminds us that it's not one versus the other - it's more about pulling in the pieces of each that work for you.