NtEd - Music Score Notation editor.
iHandy Carpenter - An handy carpenter tool kit right on your device! There are 5 tools in this Carpenter tool kit:
Sibelius - Sibelius is a virtual score creation tool which allows composers to easily create new piano scores, developed by Avid.
Angle Finder™ - Angle Finder™, now rebranded to Protractor+, is an app that offers a handy protractor tool on your phone.
DaCapo Editor - DaCapo Editor is a free Open Source music sheet editor which allows to easily create nice looking partitions. It is available as a web application as well as a desktop application for Windows, MacOS and Linux.
Pocket Ruler AR - Pocket Ruler AR is a pocket ruler app that lets you measure objects and distances with your phone.