Mattermost - Mattermost is an open source alternative to Slack.
MuseScore.org - Create, play back and print beautiful sheet music with free and easy to use music notation software MuseScore. For Windows, Mac and Linux.
Telegram - Telegram is a messaging app with a focus on speed and security. It’s superfast, simple and free.
Guitar Pro 7 - Create, play and share your tabs
Slack - A messaging app for teams who see through the Earth!
Finale - Finale, the world standard for music notation software, lets you compose, arrange, notate, and print engraver-quality sheet music.