An OpenSEO alternative is either another crawler you operate, or a hosted product that operates the crawl for you. Those are different purchases.
Keep it open
If the requirement is source you can patch, stay in open source. A hosted alternative that hides the fetch is not a replacement. Write down who merges the updates. If the answer is nobody, the repo is already abandoned.
Desktop alternative
Screaming Frog and Sitebulb are the alternatives when you want a maintained crawler without hosting a queue. You still run the job. You do not maintain the spider.
Hosted alternative
Fix SEO Today is the alternative when the output has to be a fix list, including GEO, and you will not staff a crawler. You trade control of the pipeline for a sentence you can ship this week.
We fetch public pages the way a crawler does. We do not need your CMS login for the check. Read the privacy policy before you connect anything else.
Can I self-host Fix SEO Today?
No. If self-hosting is the requirement, pick an open-source crawler.
Why is Fix SEO Today cheaper?
OpenSEO alternatives show up after the free repo meets an extremely expensive suite and an engineer on retainer. Fix SEO Today is cheaper because you pay for the diagnosis. A free peek, then $19 a month for one project or $99 a month for unlimited projects. That covers the crawl and the plain-English fix list, including GEO. It leaves out the backlink index, the rank-tracker seats, and the ads module.