If what you mean by "horizontal scale of writes" is a distributed database, then there is FoundationDB, which is one of the very few databases that offers strict serializability (see https://jepsen.io/consistency). But it isn't quite comparable, because it isn't an easy-to-use shiny tool, rather a database-building toolkit (hence the name).
Not a distributed systems guy, but Spanner also offers that right? Or at least I'd assume they do considering they coordinate with actual clocks so you're naturally tied with real-time.
It is now. There were a few years where it had basically disappeared (2015-2018). When Apple eventually put it back in the open-source world, it was done with little fanfare so it could be easy to miss.
Most of those solutions are not on part with Cockroach, Cockroach is basically Spanner usable outside of Google. So global transaction with cluster world wide.
Spanner is cheap in comparison depending on your storage requirements. I've seen CockroachDB quoted as 10x more, and for a product that is harder to sell to stake holders.
I do love Cockroach, but the old licensing model was pretty brutal if you required any enterprise features (ex: incremental backup).
For reference, some other data stores doing "horizontal scale of writes" ..any others I'm missing ?
* MySQL: Vitess, Planetscale, TiDB, MariaDB Spider
* Postgres: Citus, YugabyteDB, YDB, Neon
* SQLite: mvsqlite, marmot
* Document: ScyllaDB, Cassandra, DynamoDB