OpenTodoList

OpenTodoList is an open source task manager and note taking application. Organize todo lists, notes and images in libraries. These libraries are stored locally on the device as simple files by default, ensuring that you remain in control what happens with your data.

However, you can use any sync service (such as the Foldersync app) to synchronize your local libraries with cloud services as e.g. ownCloud. That way you can synchronize your libraries across devices using the cloud provider of you choice.