There's new browser extensions on the resources page. They're simple but they do the job.
Others I’ve used just get abandoned too, and as you mention perhaps the API is what’s holding them back.
The reason I thought your own client(s) may be on your todo list is that developing a great API is easier when you’re dogfooding.
I don't really understand the need for an app vs. a website that works well on mobile (my current project). Since many people like standalone apps, I'm clearly missing something, and would love to understand better what the advantages are there.