Notational Velocity
Notational Velocity is a computer program for Mac OS X used for notetaking. It allows users to create notes using solely a computer keyboard and search them using incremental find. Other features include database encryption, basic text formatting, tags and spellcheck. In addition, users can synchronize notes with Simplenote and export to a variety of formats, including plain text, HTML and rich text. It has been recommended along with Simplenote as a solution for taking and syncing notes by both Wired and Lifehacker. Notational Velocity hasn't seen any development activity since September 2011. In 2013, Elastic Threads (David Halter) and Brett Terpstra created a fork of Notational Velocity with added functionality called nvALT. nvALT was last updated in 2017. In 2019, Brett Terpstra and Fletcher Penney started working on a replacement for nvALT called nvUltra. As of 2023, nvUltra is available as a closed Beta release. See also 
Comparison of notetaking software

References 

MacOS-only free software
Note-taking software