A short, practical one today.
If, as I do, you enjoy the flexibility and features of gmail, please consider adding rapportive (an add-on that works in Safari, Firefox, and Chrome).
In a nutshell it displays information in a sidebar about the person who sent or received the email you are looking at, including social media, previous email exchanges, and photo. It’s a godsend if you can’t quite remember who someone is, and helps you keep up with what people are doing.
Oh, and did I mention it’s free?