Acid Morse Trainer
Back in 2004 I wrote a very simple CW trainer which later I gave away as freeware. Here's the feature list :

That's how the output screen looks like :

You can get the file here.
- 4 waveforms to choose from
- variable speed ( 40 - 300 LPM )
- variable tone ( 100 - 1000 Hz )
- allows combinations of chars for specific training
- resonant low pass filter ( variable cutoff and resonance )
- variable volume
- basic AR volume envelope shaping

That's how the output screen looks like :

You can get the file here.