Yes, Open Whisper Systems. Signal is open source and meant to be accessible. There's also ToxCore -
https://github.com/irungentoo/toxcore - which I have no experience with and I've heard sometimes the community is a little trollish, but it has similar goals.
Remember, any privacy project could use this help. All of them want to be accessible to the end user, including old-school tools like GnuPG. Often times these security engineers aren't very UX oriented and we like our command lines. Build good interfaces on top of them. Although a shitty name, Felony looked good for this: https://github.com/henryboldi/felony
Someone else asked a similar question in another Ask HN earlier, and I replied with this:
> Welcome to the fray.
> First: decide what your skills are, and where you can contribute.
> Try the Tor Project first:
> https://www.torproject.org/getinvolved/volunteer.html.en
> The community is great there and very accepting of newbies that have the skills.
> Signal / open whisper systems also are open source and accept pull requests:
> https://github.com/whispersystems/
> Read the anonbib:
> http://freehaven.net/anonbib/
> Also, there are other mixnet/darknet projects that could use help, such as i2p:
> https://geti2p.net/en/get-involved
> And if you want decentralized, mesh communications, cjdns and the Hyperboria experiment:
> https://hyperboria.net/
Get involved with any of it. Push for the user, fight for the user. Make it accessible and message the shit out of it. All of them have their merits and any work toward any of them is progress.