MemoRekall is free and open source.
The source code is available here.
If you wish to contribute, make a fork, integrate MemoRekall into a local development environment or if you’re simply curious, here is the repo on Tétras Libre’s (the team responsible for the development of MemoRekall) instance of gitlab.
You can also participate in development by publishing issues on this repo (you can make suggestions for features or report bugs). For any other suggestions, contact us.