What are some alternatives?
When comparing Diaro and Day One, you can also consider the following products
Journey - A diary that keeps your private memories forever.
Penzu - Keep all of your thoughts in one place using Penzu. The app is similar to a journal that you might write in but with a few modern touches that allow you to do everything from sending messages to decorating the pages.
Daylio - Daylio enables you to keep a private diary without having to type a single line.
Evernote - Bring your life's work together in one digital workspace. Evernote is the place to collect inspirational ideas, write meaningful words, and move your important projects forward.
Momento - Momento is a unique diary/journal writing app for iPhone & iPod touch, which provides a quick...
RedNotebook - RedNotebook is a software that format, tag and search entries and add pictures, links and customizable templates, spell check notes, and export to plain text, HTML, Latex or PDF.