This plugin makes Roundcube webmail http://roundcube.net/ use the client-API of Mailvelope https://www.mailvelope.com/ in order to create handle OpenPGP emails. It's useful only for users that have Mailvelope installed in their browser. Users without Mailvelope won't note any difference.
Confirmed to be working with Roundcube v1.0.x.
To use the plugin drop the code into Roundcube's plugins-folder and enable it in Roundcube's config. E.g.:
cd $roundcube/plugins
git clone git://github.com/posteo/mailvelope_client
vim ../config/config.inc.php
Any contribution is welcome! Feel free to open an issue or do a pull request at github.com.