Curio Most powerful digital whiteboard ever. It makes great user story boards and release plans. People behind it are extremely nice and responsive, they dedicate a lot of attention listening to peoples' cases for further upgrades.
Emacs doesn't need any special introduction I guess. I've been using Emacs since 2009 for everything related to text and communication between text-based programs, yet cannot recommend to anybody to invest their time into it.
Mutagenseamlessly sync local files and maintains network tunnels with remote machines. I use it to keep code local while running it in appropriate environment and scale, mostly on Digital Ocean droplets.
Polypaneis a recent addition to my stack, it is a fantastic browser that helps building websites that works great on every device. I really enjoyed discussing feedback with the founder who is very responsive.