Slashdot has a comparison of a few alternatives. My preference is Briar as my user name would indicate!
BriarTalker
IMO, Briar is the best option. I recently started a project to connect users in the Briar private groups and forums. We just need to get enough users active to get the network effect working for us and not against us.
Now I'm wondering how much of the price we pay is due to the cost of manufacturing and how much is just a bunch of middle-men driving up prices. Maybe this is just a case of a bunch of shell companies organized for military purposes but I'm going to guess that the practice is relatively normal enough that it didn't raise any red-flags among the other firms involved.
There is a desktop app. I am hopeful with EU cracking down on Apple will eventually result in Briar becoming available on that platform. I am working on an idea to connect people on Briar for use of the private groups and forums so you might check back with me in a few weeks to see where that's at.
Now that most of my friends and family are using it, I'm on Briar Messaging every day. Since there are no central servers, is entirely encrypted, and runs on the Tor network, I think it is probably the most secure messaging platform out there. It also has private groups and forums but I am not yet involved in any of those outside of a couple of small ones that are just for sharing family news.
I think the key is getting a core group of users in your friend/family community using it. I got all my family using Briar and now some of their friends are on it too, just because they knew people using it. IMO, Briar is the best message platform out there and I'd love to see more people using it.
A lot of these services have a network effect. Being the only user on the platform doesn't create any value. You need to have someone on the other side to interact with. I was able to get my entire family using Briar as an SMS replacement. I'm working on a few ideas for networking people who want to use Briar with each other so we can have private forums for an array of interests.
Another idea I thought of was copying static websites (won't work for websites that are a service) and then putting them out there as a .onion website using OnionShare. I think it would be a good idea to create sites that are lists of .onion sites or add them to Ahmia (http://juhanurmihxlp77nkq76byazcldy2hlmovfu2epvl5ankdibsot4csyd.onion/) for people to find.
We might not be able to build a web that looks like the web of today but we can build one that's on par or better than what existed in the 1990's. In a lot of ways, that could be a very good thing.
I read somewhere that these sites were intentionally positioned near population centers so that an attack on these nuclear facilities would also create a greater disaster.