A little niche, but https://run-in.app is an online encounter manager for DnD 5e that I've been (slowly) building this year. I initially built it because I was dming a one-shot for some friends and got overwhelmed tracking the health and position of 6 enemies + the party on pen and paper.
I wasn't happy with the solutions I found to this online, and thought it'd be fun to try and build one myself.
The main features for creating and running an encounter are ready: 1. Adding any 5e SRD mob or a custom mob to battle maps 2. Dragging mobs around the battle map 3. Turn and health tracking 4. Status effect tracking
But there are a few bugs to iron out, and more features to come!
As a heads up, if you visit the site and get a cold start of the container, it might take a while to be properly interactive. This is, unsurprisingly, the first thing to fix on the roadmap.