More information can be found in the official release announcement, and on the release information page.
Google App Engine Now Contains Python API
Google released version 1.5.1 of their App Engine SDK, which will contain the open source ProtoRPC framework as an official Python API. There's also a Geolocation header with each client request, which will try to identify the country that the request came from.
Download the new version of Google App Engine here.
Mozilla Launches Firefox Add-on Tools For Developers
Click here to download the Add-on Builder and the Add-on SDK.
Second Version of iOS 5 Beta Now Available
Apple released their second beta of iOS 5 for developers over the weekend, which includes their new Wi-Fi sync feature, that transfers data wirelessly from Mac to all Apple mobile devices.
Click here to see a full change log (via BGR).
Click here to access the new iOS 5 beta (registration required)