By Tom Beckman announced on Google+
Instructions at linuxg. How to install:
$ sudo add-apt-repository ppa:noobslab/apps
$ sudo apt-get update
$ sudo apt-get install indicator-synapse
More at webupd8.
How to install:
sudo apt-add-repository ppa:versable/elementary-update
sudo apt-get update
sudo apt-get install cable
By Birdie team
By Nathan Dyer
How to install:
sudo apt-add-repository ppa:nathandyer/vocal-daily
sudo apt-get update
sudo apt-get install vocal
By Tom Beckman
http://elementarytips.blogspot.fr/2013/02/lightread-redux.html
By Tom Beckman and Edward Gotwig
How to install:
sudo apt-add-repository ppa:gotwig/weekly
sudo apt-get update
sudo apt-get install gazette
More info (in French)
By Tom Beckman
How to install:
sudo apt-get install eidete 
By Shawn McTear
https://plus.google.com/108592136122613230661/posts/BnSgmVggrFY
http://www.elementaryos-fr.org/manuel-du-developpeur-elementary-disponible-google-play/
Updated here
By Kiran Hampal
By Dane Henson
How to install:
sudo add-apt-repository ppa:agenda-developers/daily
sudo apt-get update
sudo apt-get install agenda-tasks
