Women Hack for Non-Profits http://www.womenhackfornonprofits.com/ are looking for volunteer designers, ux and everything else web dev related to mentor volunteers and help work on projects that help charities.
The organisation is only a year old but there are 9 projects that require help and more projects on their way. Contributions can be as simple as advice on Slack to full blown workshops, talks and mentoring. I have been part of the organisation since the very first meetup and it has helped me develop the skills I needed to move in a front end dev career. This is a great opportunity to help women improve their skills while they work on projects for a good cause and perhaps to practice your talks/workshops and materials on a very keen/grateful audience :D
The majority of the volunteers are in London and meet face to face, attend meetups and workshops but we also have some remote volunteers that we communicate with on Slack and Google hangouts.