Here is a list of popular apps that I use:

www.evernote.com – this app is used by millions world wide as their “second brain” to hold almost anything that is digital including, PDFs, MS documents, typed notes, photos, audio files (can be played within the app), video files (must be played outside the app), hand written notes. You can categorize notes with Tags and place them in Notebooks and related Notebooks into Stacks. Evernote continually improves functionality and streamlines the appearance. Works easily to synchronize across multiple operating systems and on mobile devices. I have used this since 2008 and manage nearly 7,000 Notes. It’s easy to get important documents, receipts, bill, etc with an app for iPhones called Scannable. It lets you scan documents as images or PDFs and they go directly to Evernote. 

www.todoist.com – this is a very popular app for creating task lists, with filters by priority, date, label, color, etc. Straight forward with an easy learning curve. Works well across different platforms and mobile apps. I use it daily

www.trello.com – a popular project manager when working with teams. 

www.busymac.com – this site offers an add-on to upgrade your Mac’s contact app and calendar with a number of features to make life easier.

Some new ones that I am investigating:

www.asana.com – a popular project manager when working with teams. 

www.notion.com – a new entry into the note taking world with more flexibility than Evernote but requires a longer learning curve.

www.obsidian.md – another new entry into note taking with two-way linking of notes and mapping/linking of notes. All notes are in Markdown format so they can be read by a variety of apps. Requires work to learn the nuances but appears to appeal to creators, writers, and researchers. The graphing function is amazing when you begin to see clusters of notes linked and appearing to be “constellations”. You’ll be impressed to see the visual connections of your file links.