As IndieDevs/ founders, promoting your tool is a hard task, as we do not necessarily have the qualities of the marketer. We build things, but then realize it needed to be sold too, to sustain.
I personally use this list, to list my tools, get some acute visibility and some good backlinks, which I can then use to start my content marketing or SEO of the tool. The backlinks are of high quality because of high DA sites.
You can get this list for free from here - 101+ Sites for Listing
Some of those sites are:
Get direct links to all through here