Standard Notes is an open source, plain text note taking tool. The authors of the application place emphasis on security and long lasting.
Security is provided by fully encrypting all notes locally before they are transmitted and stored on their server. A third party security audit 
was last performed in August 2017. While I like that at least one audit has been done, I am a bit concerned that audit was not performed in 2018.
By longevity, the authors state:
>Our revolutionary, paradigm-shifting 21st-century business plan is to keep your information ready for the 22nd century. The notes you write now should be there for you in a 100 years. That's our killer app.
The free version provides all of the core features of the app that I think one would want. Full encryption, support for all platforms, unlimited syncing and no limits on data storage, and number of devices you use.
The paid version costs $4.17 per month and provides extended features including the ability to encrypt attachments, note version history, extensions , and two-factor authentication. If you pay for a five year plan you can get a reduced rate of $2.48 per month.
Given how much one gets for free, I do wonder how many opt for the paid version and if that adequately compensates the authors to continue hosting and do further development.
One can host Standard Notes on their own server and the author provides instructions for building your own using EC2 and Nginx . Better yet, there is a pre-configured AMI template to get you started with your own EC2 server.
Instructions exist for using Docker , but they don't appear to provide containers via Docker Hub, which defeats the purpose of using Docker. They also provide instructions for self hosting on Heroku . Unfortunately, I don't see generic installation instructions to build your server on Digital Ocean or another service, although I imagine people with experience can translate from the EC2 build instructions.