Apps we use day-to-day
I think that apps are an integral part of our lives, so I do spend time finding out what apps are out there, and trying out new ones. Here I've put together a list of what I recommend, based on my own usage.
I advise that you subscribe to a newspaper, to get well-written, informative and accurate news, rather than relying on social media. I choose The Economist as I am an economist, so their news is important for my job, and also I hold the quality of their news in high regard. It is ethical to pay for the work that other people do, including journalists, authors and creatives. Whilst gen.lib.rus.ec often provides useful information when I want to find out what's in a book (or have the convenience of an e-book), one can justify subscribing to a newspaper and purchasing other books by claiming that it offsets the unethicality of accessing Library Genesis, in some sense.
I need a to-do list app that syncs across my devices. Todoist offers a lot of features, such as sharing a project with someone else, or generating sub-projects or sub-tasks (or sub-sub-tasks, etc.). The premium version lets you comment on your tasks, with the option of adding files, audio, etc. But perhaps the best feature out of it all is that each task can be assigned a "priority" level out of four, then you can simply view all your tasks ordered by priority, which collects together the most important tasks from across your projects.
I use Todoist to plan what I think is most important for me to do in my life, although during each day I rarely add minutiae.
I think it's important to sync one's files with a cloud storage server. I've used Google Drive for a long time, because it's popular. Seeing as I am experienced at using Google Drive and G Suite to improve productivity and collaboration, I provide support for this (on a voluntary basis) on WebApps.StackExchange.com. Syncing Google Drive with one's computer isn't supported on Linux though. InSync is a third-party sync client that can work on Linux. However, after InSync repeatedly deleted some of my files without me wanting it to, I decided to switch to Dropbox (which is supported on Linux). The feature that I like the most on Dropbox is that one can rollback a whole chunk of one's files to a previous date, which guards against ransomware (or mishaps). Google Drive doesn't offer protection against ransomware, as each encrypted file will automatically sync with the cloud server, and it would be near-impossible to rollback each individual file, one-by-one.
is a fun way to learn a new language.
Xodo PDF reader
I use Xodo on my tablet to read PDFs. With Xodo, you can change the colours on the PDF, for example by making the background black and the text white, so that it is easier on your eyes. If you use a tablet, this app makes it easy to annotate your PDFs with highlights, underlines, and boxes. Comments can be attached to any annotation. Xodo also works well on a Windows computer, but it can't open two PDFs alongside, so if you want to do that, use Sumatra PDF. Sumatra PDF is a lightweight PDF reader, which lets you overwrite a PDF while it's open.
You can sign PDFs electronically with Adobe Reader's free "Fill & Sign" feature, which lets you insert an image of your signature, or just type your name in handwriting font. This saves you printing out and scanning forms (which ends up in lower quality).
If you want to learn LaTeX, I recommend that you get Kopka & Daly's Guide to LaTeX.
I think that it's better to use Slack (or Discord) in a work context, as WhatsApp is too intrusive on one's personal life.