Here's what I wrote about it when I released it out into the wild, way back when:
Markup Processor is a powerful html/script editor written expressly for me! But maybe you'll find it useful too... from beginners, intermediate to professional web builders, Markup Processor is a web editing tool for anyone creating web sites or authoring scripts. Markup Processor is a fast, lightweight product months in the making but please bear in mind it has been designed to do just what I want... no-one else! In other words, please feel free to suggest changes but I have the final say on what makes it into the product, okay?
Best of all, Markup Processor is lightweight, and loads a lot quicker than many comparable programs. I never did finish it though, so it's only fair to also mention the shortfalls: for a start, there's no tag completion, a feature I'd really want if I was starting this from scratch. The biggest omission though is the lack of word wrapping, but if you can live without that, Markup Processor is a handy bit of kit. I use it all the time... but then I would, wouldn't I?
As I said then, it never got finished quite as I'd like. And looking back, I regret making it insert HTML tags in uppercase rather than lower - whatever happened to standards compliance?! But never mind. I'm starting to mothball the old website this was previously publicly available on, so I'm making it available here instead, for posterity: its own little software cemetery.
Anyway, enough history. Here's the download if you actually want to give it a spin. To install: unzip the download (try 7-Zip in the unlikely event you need help with that), run the MSI, accept all the defaults. Job done.
Oh, and in the even more unlikely event that you use this enough to need support, well, you could ask in the comments below this post. If I can remember, I'll try to help. No promises, mind.