Paul Jones has this new post on his blog about the release of two new versions of Solar (back to back) - versions 0.21 and 0.22.

I released Solar 0.21.0 yesterday, and a quick followup 0.22.0 today. The rest of this entry covers highlights for changes in both versions. The main highlights are three new classes (Solar_Struct, Solar_Sql_Row, and Solar_Sql_Rowset) along with a backwards-compatibility break to how classes store their default configuration values.

He lists out the updates, describing the changes that were made to things such as the $_config system, Solar_Sql_Row, and User-Defined Row Classes. There are also some interesting additional comments on the release.