CWTERM was one of the top choices in qrq cw sending software during the DOS computer era.
DOS seemed to be able to take complete control over the serial port and therefore, the timing and accuracy
was very good when sending qrq cw to your rig via the RTS or DTR serial port pin - TO - cw keying circuits.
Check out the author's(W1HKJ) site where he has a CWTERM download available
DOSBOX. I have tested it for qrq with DOSBOX and it is working on my windows 7, 64 bit laptop very well.
I was amazed at how good the qrq timing is when using cwterm/dosbox with a usb2serial port adapter.
The CWTERM manual is included in the download file as a DOC and PDF file.