Diaro is described as 'is designed to record your activities, daily events, appointments, experiences, thoughts, secrets and ideas throughout the day and sync data across all your devices. It is the easiest and most secure way to keep a diary' and is an app in the Office & Productivity category. There are more than 100 alternatives to Diaro for a variety of platforms, including Android, iPhone, Windows, iPad and Mac. The best alternative is Joplin, which is both free and Open Source. Other great apps like Diaro are Standard Notes (Freemium, Open Source), Evernote (Freemium), CherryTree (Free, Open Source) and Trilium Notes (Free, Open Source).
NixNote, formerly Nevernote, is an open source client for Evernote . It is written in Java so it will also run on Windows & OS-X, but the primary focus has been to try and get a usable environment for Linux.
A simplified, RedNotebook-type journal/diary app. With a focus on minimal design and a distraction free writing environment. Makes a folder full of dated text files that are easy to access even without the journal program.