TL;DR You have no responsibility to keep coding, but you do have a responsibility to transition the project to a new maintainer if someone sufficiently competen

TL;DR You have no responsibility to keep coding, but you do have a responsibility to transition the project to a new maintainer if someone sufficiently competent volunteers. As many others have already mentioned, it is very useful to clarify in the README what the status of the project is. Something I would like to add is that if someone else comes along who offers to take over maintenance, that is a useful thing which you should probably accept, and then you should update your README to point to the new official maintainer. You can also explicitly mention in the README that the project is looking for a new maintainer, which to me always seems a bit friendlier than just stating you've abandoned the project. Even if you don't officially pick a new maintainer for your project, if a couple of forks spring up on github consider linking to them from your README if they still seem active after a couple of months.