Ask tech-bloggers to use your software and review it.
November 29, 2016
Donate your skills to non-profit sites in exchange for a link.
November 29, 2016

Donate to a charity that links back to their donors on their site.

Donate some of the profits you generate every month to charity. Being involved in this activity is great for promotion in the media and for the good will of clients: they will feel like they’re helping out the charity by purchasing from you. Besides, charity sites may list their donators in a special section of their site.