[Sparrow]

It's true that NT is not rock solid but I've had NT 6.5 running for several days gathering data without any problems.
There are some minor glitches(I'm using the beta right now) but nothing serious.

Where it shines are the charts they look really good, supports a lot of data feeds and brokers(only QT has more imo) and the programming capabilities are awesome.

Ninjatrader is one of the best among the free charting platforms, and is just lacking a few features that I'd love to have (multiple timeframe/instrument indicators/charts).