MIDI Scale Enforcer

[xylyx]

Sonar 5 (and I would think v6) has a scale lock on midi tracks built-in.

[nuffink]

I don't know of any sequencer with scale lock.

Notrons have a force to scale feature.

ableton live has an internal midi plug that will also force to scale.

Sonar 5 (and I would think v6) has a scale lock on midi tracks built-in.

My mistake, I should have been more explict (oo-err missus).

I'm not familiar with Notron, but the Sonar and Ableton scale locks both work in a similar manner. They lock one scale to a midi track. This means that you can lock (for instance) the Major scale over an entire track or the Minor scale over an entire track. Fine as far as it goes but a bit limiting.
Take the C Major scale as an example. This kind of scale lock will force you to play...
C Ionian
D Dorian
E Phrygian
F Lydian
G Mixolydian
A Aolian
B Locrian
... because these are the diatonic modes of C major.
This is ok, often you'd want to do this but it has its limitations. A Aolian contains a minor 9th interval, a so-called avoid note. E Phrygian contains two. An experienced player might decide to play the Dorian mode (which has no avoid notes) over both the A and the E chords, avoiding the avoid notes as it were.
Playa allows you to do this and much more.