Earlier in the year Giuseppe IK8YFW shared a project he has been working on to make a cheap and simple DSP receiver based on the arm cortex stm32f103 processor. This module costs less than two US dollars in Far East online shops.
He has implemented two narrow CW filters of about 300 and 700 Hz and two SSB filters with widths of less than 2200 Hz, and less than 3300 Hz. He also includes a 6-level noise reduction algorithm.
The project is a very cheap solution and is suitable to embed in every QRP project. Details of the project and code is available on github. It is still at an experimental stage but is worth looking at by experimenters.
The project can be found here:
Some test videos of the DSP in action can be found here: