Not quite without flash, but check out Flashpoint.

https://bluemaxima.org/flashpoint/datahub/Game_Master_List

https://bluemaxima.org/flashpoint/

Seconded, I missed that time-sink game so much, haven't been able to find a replacement.

For some reason all the newer tower defense games use a fixed playing field whereas the original DTD allowed you to build your own defensive walls.

Edit: We really need a Flash Archive

Building your own walls was very exploitable, so I can understand removing the ability.

There are some fantastic TDs that allow you to build your own walls in an open field, they just need to be explicitly balanced around that.

Besides Desktop TD, the other main classic of that subgenre is Bubble Tanks TD: https://armorgames.com/play/4962/bubble-tanks-tower-defense

I haven't tried this, but you could try the Ruffle browser extension. I think it's designed as a drop in replacement for the flash player.

https://github.com/ruffle-rs/ruffle/wiki/Using-Ruffle#browse...