To add to ph03n1xii's great explanation, this can be done with nearly any blockchain. However, considering large amounts of entries, Factom is a much more cost-efficient solution. The cost of making an entry is kept at about a tenth of a cent. Entries are made with a non-transferable token called Entry Credits, and Factoids are burned to create Entry Credits. Factoids can freely fluctuate in value while Entry Credits are held at that tenth of a cent. There are only about 8.75 million Factoids. There is no mining involved, Factom is anchored into other blockchains like Bitcoin, essentially piggybacking it's vast security. The protocol fully works, but it's still under development. The supply of factoids will not grow until development is complete.