I am the maintainer of a project which has a large non-technical userbase. I've been maintaining it for about 4 years now and adding new features as they've been requested.
I'd like to move on to other projects now and stop developing for this application. Because of the non-technical nature of the users, there have been very few code contributions in the past. I don't believe I will be able to find anyone else to take over the project in my stead.
Bugs, issues, feature requests – these are still coming in. I am still responding to emails for help, as I am not sure if I should ignore them, tell them that I'm not working on the application, or if I should respond to emails in only certain cases.
What is the best way to 'abandon' this project, but still let users use the application?
Update (July 2016) – It didn't go as planned. I made an announcement in the README and soon after, I started receiving contributions of a more substantial nature. Pull requests with bug fixes, features, documentation, issue activity. Since then, the project has felt 'reinvigorated' and I'm now happily maintaining it along with newer projects. I have collaborators as well. At a guess, it may have been the kind of contributions which were affecting my view of the project and with the quality of contributions improving, it didn't feel like a chore any more.
Best Answer
I'm guessing this is not a project at a workplace where you are a paid employee and something you do in your spare time for free?
If you are making no money from this, then clearly there is no incentive for you, and no incentive for anyone else to come in fresh to deal with it. (unless maybe it is for a charity or similar voluntary organisation)
As an alternative, why not look at the possibility of adding paid for features.
This way you may have some incentive to continue. You might find people willing to pay, especially when the alternative is for the system to stop being actively developed. (of course people may abandon your system, but what do you care, you already aren't being paid).
Another option could be to use the project to learn new technologies? Is it a website? Upgrade to the latest technology? Convert from Asp.Net to MVC4 for example? build a mobile version, make it service based and create an iOS app front end for it?