I don't know. We tried looking for alternatives when we were a bit down in the gutter with our Jenkins setup, but were even more disappointed with the other options.
Instead, we now use Jenkinsfiles everywhere, or pipeline scripts where we have scheduled stuff. That's working well enough so far for our small team.
The things Jenkins provides can be difficult to find elsewhere. For example, we spin up an EC2 slave for most builds, but sometimes need to then take the result and deploy it from another (static) node because of network restrictions. Stuff like git access, the credential store, moving stuff between nodes just works everywhere.
Most of our builds are 'basically' Node.js / npm or PHP / composer, so reasonably contained build processes. It looks simple on the surface, but once you start running CI for a while you notice all the dependencies on the environment. Versions installed of PHP, Composer, Node.js, MySQL / MariaDB, Java, Ant all tripped us at some point. (Not to mention we develop on Mac, deploy on Linux.)
Instead, we now have a very basic Ubuntu-based AMI with Docker installed, and otherwise stopped depending on the host environment as much as possible. Jenkins spins up an EC2 instance when needed, and shuts it down again after some period of inactivity. 95% of our pipeline scripts do work inside a container.
Instead, we now use Jenkinsfiles everywhere, or pipeline scripts where we have scheduled stuff. That's working well enough so far for our small team.
The things Jenkins provides can be difficult to find elsewhere. For example, we spin up an EC2 slave for most builds, but sometimes need to then take the result and deploy it from another (static) node because of network restrictions. Stuff like git access, the credential store, moving stuff between nodes just works everywhere.