Nearly every platform and broker offer DOM or soon would be out of business for short-term traders.
As you can guess by the number of posts, most of the futures.io (formerly BMT) members use NT or Sierra as their primary platform.
Both are compatible with several brokers.
Regarding "demo" you normally will have to pay for any realtime data that you use (at least after some free days)
or you will be in "demo only" mode with lagged or purely fictitious data that allow you to learn the platform functions
but that have few to do with trading a realtime asset. The shorter your time frame is, the sooner you will not only
need temporary snapshots (which several brokers offer under the label "realtime"), but also tick-by-tick data.
Since "demo" doesn't mean "free" for realtime data anyway and demo trading won't teach you much about risk and money management and above all: about yourself, if you have skin in the game, you are normally better off with trading
real assets small size (like e.g. ETFs or Emicros) .
The following 2 users say Thank You to choke35 for this post: