In short, kinda. Well, more like mostly dead.
And fixing it would probably be even more effort than simply writing something new or upgrading Heron.
I used HeliumFrog for ages before recently jumping over to Heron. There's a reason it's so highly recommended.
There's also a reason it's falling out of favor.
It hasn't been updated in years, and while the author claimed back in 2012, then again in 2015, to be working on a new version, neither has yet to see the light of day. It started out great, but mildly buggy. Being free, but with all the great features animators have been looking for made it a popular choice. But as time and computers have progressed, it had steadily become more and more unusable. At least for me.
Simply put, HeliumFrog is really old and really buggy. When it works, it's my favorite animation software.
When it doesn't, well...yeah. Especially since Windows 10 came out, I've had so many issues with it that it become unusable, but I'd still suggest you try it.
If you want, I can hunt around and email you the HeliumFrog files you'll need for Windows 10 if you don't trust that site. Honestly, it's been so long since I've downloaded them that I can't remember if the site threw those warnings for me or not. (I'm thinking not)
HeliumFrog has onion-skinning, easy playback, several export options, and (the biggest advantage over Heron) 1080p recording. However, even when working "right" the settings menu tends to get stuck, forcing you to close the program to exit that, and utilities does the same.
At this point, I'd suggest Heron. It's new, clean, slick, and actively being supported and developed. I love the look, and that's it's made by a member of BiM. If you need 1080p, MonkeyJam is a good option.
However, the latter isn't as clean, the preview window is the same size as the final frame, making it really big and hard to see, and it simply seems clunkier. Plus, I've had some issues with crippling bugs since upgrading to Windows 10. However, it's a functional and solid piece of software. It's free, so it'll be easy to give it a try.