What are Indeed and Simply Hired?

They are job aggregators,  they collate jobs from various job boards, career sites and employers sites. They do this by crawling the sites and taking all the relevant information to post it into to their sites. Googlyfish however XML feeds the jobs daily  to the aggregators so your job postings are right up to date on their sites, unlike the crawling bot which could take days if not weeks to extract the information.