Platform

We've added a new webhook for when signatures are deleted from a petition. (Signers can unsubscribe from a petition, which stops them from receiving emails about the petition, but keeps them as a signer. Signers can also delete their signature (using the "Not sure what we're talking about? Remove your signature" link in the thank you for signing email). This completely removes their signature from the petition.)
When searching for a member, having a starting or trailing space would cause an error. We now strip out those spaces, making searches easier.

Petitions

When a logged in user has already signed a petition, we now fittingly display a "You have signed this petition" message where the signature form is normally displayed. In addition to just reflecting reality, this new feature also allows signers to leave reasons for signing at a later time. For members who share computers, we also include a "Not FirstName LastInitial? Log out to sign the petition" link.
As part of our new already signed feature, we've also included two new events for Segment users: "Saw petition already signed" and "User signed out from petition already signed."
We now include global custom fields in partner exports.

Calendar event uploads are now supported. More.
During the creation of petition events, we allow the event creator to email the petition's existing signers. This email is sent to the email moderation queue, where we provide a preview of the email. However, for petition events, the preview didn't match what the email actually looked like when it was sent. Specifically, we stripped out the line breaks – we don't do that anymore. TL;DR email previews should correctly preview emails.
We now include global custom fields in partner exports.

Nothing new in groups or TakeCharge.