What is ClassicPress?
Basically, it is WordPress version 4.9, the last version before Gutenberg became core in version 5.0
Created by Scott Bowler, he quickly gathered together 15 or so volunteer team members to release the Alpha version on 24 October 2018. The Beta version was released on 21 November 2018.
Using a migration plugin provided by them, you can easily convert your existing site from WordPress 4.9 to ClassicPress 1.0 and continue using TinyMCE.
Even though still in Beta version, there has been enough testing done for the development team leader to announce it is suitable for live sites. You can read more here.
This site was built using ClassicPress from scratch and other sites run by the owner have also been successfully migrated to CP without causing problems.
I have made a post here that will help you migrate to ClassicPress or install it from scratch.
Is ClassicPress a viable long-term option?
As you can read on their website classicpress.net and in their forum posts, they’re planning to be here for the long haul. Their philosophy is a “community-up” method of operation, as opposed to the WordPress “top-down” method.
Rather than force unwanted features on users, they are using a petition system. Users can suggest and vote on any planned changes. Scott is a firm believer in having a democratic system and has also registered the project as a non-profit organization, based out of the United Kingdom.
Some people at WordPress are supportive of what ClassicPress is trying to achieve, but others are angry at what they see as an unnecessary and disruptive move. WP users who want nothing to do with Gutenberg are ecstatic there is an alternative that works the way they’re used to.