I've used sleek as my primary todo.txt UI for a while now, and I'm really happy with it. If you are interested in a simple, but useful way to put together a todo list in plaintext, the todo.txt spec is a great way to handle it, and sleek is by far the nicest GUI I've found.
About a week ago, I ran into a minor annoyance with an edge use-case that I have, and I wrote about it in the sleek github discussion page. Within 4 days, the maintainer of the project had a new build ready that fixed my issue. Nobody else said they needed it, but they took the time to add the feature I requested and now my workflow is that much easier.
I know not every project is like this, or can be like this, but there's no way that something like this would get added at anywhere near this pace in proprietary software. I, for one, am super grateful that software like this and the people that maintain it exist. Thank you.
Please check out sleek!
Thanks for sharing, Markor looks promising
Markor also has support for Zim Wiki, so I tried it out with some files from my Zim Desktop Wiki notebook, and it sortof works! Markor renders correctly, though I had some problems getting embedded images to work, because Markor didn't find the images using the same relative URLs as Zim Desktop Wiki uses.