It's a completely different project. From the user perspective:

- DD-WRT contains a lot of features that are exposed on the UI, but the project is almost dead, with the last stable release being in 2020, but activity died probably a decade ago.

- Open-WRT is very active, but the UI is an afterthought. The feature set is barebones and you need to install plugins for a lot of things - requiring command-line configuration. The Gargoyle project is a more ui-friendly fork, but it's also not really active, and supports a narrow set of routers.

- Besides Merlin, for Broadcom/ASUS, Tomato (and derivative projects) is an alternative, but newer routers are not really supported it seems.

I just checked out Advanced Tomato for a number of routers and the latest update was late 2017. I stopped using Tomato by Shibby for the same reason. Even if the possibility of adding features dried up, I'd have expected some kernel, security, or GUI updates over that time.

Tomato firmware seems to jump to a new project every few years, the version being updated now is called FreshTomato with the latest release being from December 2021.

Appreciate the pointer, kind stranger! I'll have to load this up onto my Asus router that is no longer supported by Merlin. I hate that the stock Asus firmware doesn't let me monitor IP traffic per client. This looks to be supported by FreshTomato.

Perhaps the biggest difference is DD-WRT will accept binary-blob drivers for some SOCs / Wi-Fi chips whereas Open-WRT won't. This is notably problematic for Broadcom powered devices where the result is often that Open-WRT cannot provide 5 Ghz and 2.4 Ghz is sometimes spotty.

I'm having trouble finding any definitive information about it, but a while ago there was some issues with DD-WRT not being fully open source, I forget the specifics. The closest reference I could find just now was the Wikipedia talk page for ddwrt