Freenom is a free domain registrar, providing .ml/.tk/.ga/.cf/gq domains for free requiring each domain to have a publically hosted website (either on HTTP or using HSTS to force HTTPS) and be manually renewed every 12 months.
I recommend using Cloudflare as the nameserver for a domain if anything more than just a single static ip is required.
You can only renew free domains in the last two weeks of each registration period.