Just ahead of Facebook's f8 Conference, Google has announced nine new features for Google Plus, and there are some doozies. First of all, the social network is now open to the public. No sign-up required. Just go to google.com/+ and join the party. (New to Google Plus? Here's how to use it.) For the past 12 weeks, the network has been in "field trial" mode, but Senior Vice President of Engineering Vic Gundotra says that it is now "ready to move from field trial to beta." Open sign-ups is touted as the 100th feature of Google Plus.

Hangouts - the video chat feature - have come to mobile, currently supporting Android 2.3+ devices, and iOS support is "coming soon." Hangouts also now have an "On Air" feature, which allows any Google Plus user to tune in and watch. Furthermore, Hangouts now offer screensharing, a shared sketchpad, and names for Hangouts. But perhaps the killer app is Google Docs in Hangouts, which will open up the possibility of live collaborative work (especially once Google Apps accounts get access).

The big announcement for developers, following last week's initial opening of the Google Plus API, is the opening of a "Developer Preview" of the Hangouts API, which will allow third-party developers to implement the same basic set of capabilities as the existing YouTube integration uses. The announcement calls it a "basic set" of APIs, but it's a big step up from what was announced last week.

Finally, the update also adds native search to Google Plus, which turns up Google Plus content as well as stuff from around the Web for easy sharing.

Conspicuously absent? There are still no brand pages, and Google Apps accounts still can't use Plus. The latter is especially frustrating, since Google Docs in Hangouts will dramatically expand the possibilities of using Google Plus for work.

Which features are you most excited about? Tell us in the comments.