Companion apps help us manage the items, progress, and loot during our time. There are a plethora available to us, and so let's look at the ones worth using.
#4) Destiny 2
This is Bungie's official companion app. Up until recently there was no real reason to use Bungie's own Destiny companion app, that is until around Season of the Hunt when they allowed you to obtain bounties from within the app. It's a huge time saver, and worth the install.
Quickly pop in and visit this single page that best lays out the next tasks/missions you should complete in order to power level most efficiently. Simple.
#2) Braytech
With lowlidev/The Director no longer being supported, they moved to what is now Braytech - and many of the same features remain. This one is great for a number of reasons, including the ability to see the locations of missing artifacts/objects for quests you are following. Corrupted eggs, anyone?
#1) TIE - DIM (Destiny Item Manager) & Ishtar Commander
Bungie has always embraced the community and the huge support Destiny has with the many unique companion apps available. The 2 best that come to mind are DIM & Ishtar. You really only need to use one of the two, but both had to be mentioned. Follow progress, triumphs, swap/manage weapons, create custom load-outs, etc. The list goes on. Both look great and either one is a must have.