free and working, huh? If you find such a tool share it with us
This being said, there are (or used to be, I'm not sure if there still are) indexing tools in the marketplace that you can try for free. Look them up in these forums:
https://www.blackhatworld.com/forums/misc.18/https://www.blackhatworld.com/forums/seo-link-building.43/https://www.blackhatworld.com/forums/seo-other.199/
@Steptoe had also recently updated his review of the latest working indexing services, and some of them are quite affordable if you ever manage to treat business like a business. Have a look at the review here:
https://www.blackhatworld.com/seo/2024-bhw-indexer-study.1572212/
Last but not least, for what you need indexing services for (to index domain names every now and then), I think paying for an indexing service is overkill. Just try to get some traffic to those domains and google will pick them up in no time. Google loves popular sites, so try to get a few 100s of LEGIT visitors a month and make sure the domains are not tagged with noindex and they should index automagically...
You could also try to share them on social media (facebook, instagram, pinterest, reddit, etc). Sometimes it does work, it's happened to one of my fresh domains with Pinterest about 3 years ago, I had just set a new site on it (I think it was in food recipes niche, but I don't remember) and within 3-4 days of it getting 50-60 visitors a day it was already in google just because of the Pinterest traffic alone, so you don't have to stress about indexing if you do the right things
But the trick with social media, from what I know, is to make sure you share the domain from aged and active accounts, otherwise it's hit and miss...