mutt is an amazing terminal mail client. It is incredibly fast and customizable although it lacks certain features most people are used to get from their mailing software in 2020. It is however only sparsely developed which is why I use the great neomutt fork, which comes with a few common patches to simplify usage. Last year the developers behind neomutt started to apply a greater amount of patches to the original mutt source code.
Umatrix is in my opinion the best tool to stop third-party trackers and any resource loading from external sites during web browsing. Since the matrix overview can be used quite easily to unblock certain trackers I use the default setting of blocking every external page resource. This can lead to problems when a website uses popups, e.g. for third-party logins, since firefox only shows a reduced taskbar when opening a popup.
Since Ansible version 2.4 the vault IDs became quite powerful. Together with a password manager like gopass automatically decrypting vaults became quite easy, although a bit of manual work is required.
Visual Studio Code is a great editor, Okular a great PDF Viewer. To make them work together, a little bit of config is necessary though.
Background I love my Yubikey. Besides using it for local authentication it also contains my PGP key. By using the awesome pass password manager (or more accurately the go rewrite gopass) I do not have to write passwords into config files any more but just configure the correct call to pass and the rest is handled by the system. In case of email this worked really well as long as I was using offlineimap.