sensetalk-mode
Sometime around 2018 I joined a testing team that was using a tool called Eggplant Functional. The scripting language, SenseTalk, interested me because it has a long history. Back when I was first experimenting with Emacs Lisp (early 1990s) SenseTalk was being leveraged on the NeXTSTEP platform. Having used GNUstep for a while, I was more interested in Eggplant at that moment for its history than for its functional purpose.
Once I started using the tool and learning SenseTalk, I realized I couldn't write code without being connected to our VPN behind which the license server lived. I searched everywhere, on the Eggplant forum and elsewhere, but due to the way Eggplant's own script editor works against the SenseTalk compiler, nobody seemed game to offer up a plugin or similar for folks writing automation test code. I found plenty of Emacs major modes for other members of the xTalk family and considered cannibalizing one of those, but in the end it was clear this would have to be from scratch, and very intentionally written from the perspective of an Eggplant Functional user.
It took a long time but I finally wrote a usable Emacs mode in the form of sensetalk-mode, but before I completed it Ricardo Magana released his VS Code plugin Eggplant Functional Workspace, and then the next year came the official Eggplant Studio plugin for VS Code from Keysight. Now, I'm native Emacs but I did give both of these a spin and actually use Eggplant Studio on VSCodium. But I'm stubborn and will certainly keep working on sensetalk-mode until I get everything I can out of it.
I have no idea how long Eggplant will be a part of my toolset but after eight years of use, I'm definitely having a more personal relationship with it and I think that shows in the tools I'm writing for it. Eggplant runs on Linux (Ubuntu and Red Hat) so it's natural to leverage the power of Emacs Lisp for system calls and Emacs as a code editor. However it turns out it was an incredible learning experience and I can't wait to work on my next major mode for Emacs.