When comparing Semaphore CI vs Drone.io, the Slant community recommends Semaphore CI for most people. In the question“What are the best continuous integration tools?” Semaphore CI is ranked 10th while Drone.io is ranked 11th. The most important reason people chose Semaphore CI is:
Whenever a new push is made on GitHub or Bitbucket, Semaphore automatically runs tests on that branch.
Specs
Ranked in these QuestionsQuestion Ranking
Pros
Pro Automatic Testing
Whenever a new push is made on GitHub or Bitbucket, Semaphore automatically runs tests on that branch.
Pro Free for open source
Semaphore supports open source and offers unlimited open source projects.
Pro Complete customer support
Semaphore offers all-around customer support for its commercial users.
Pro Free 100 builds per month for private projects
Semaphore offers 100 builds every month for private projects. This package is free for an unlimited time and offers: free & unlimited deploys, unlimited collaborators and running tests in parallel.
Pro GitHub integration
Projects can be imported from GitHub and Semaphore will automatically connect with that repository, once that's done, it will automatically trigger for every code commit.
Pro Docker support
Out of the box Docker support. Additionally, Semaphore can cache Docker images by using included docker-cache commands.
Pro Easy to configure
Semaphore is quite easy to configure and work with. It easily integrates with GitHub and a first build is only a few clicks away.
Semaphore is configured using .yaml configuration files which can be added from the web UI. There are a lot of tutorials out there that help developers configure Semaphore to their preference.
Pro Integrated with GitHub, BitBucket, and Google Code
Drone.io integrates perfectly with GitHub, BitBucket and Google Code.
Pro Easy self-hosted setup
Drone can be easily set up locally: all that's needed is Docker.
Pro Docker integration simplifies deployment
Drone uses Docker containers to build and test code. Using Docker containers makes it easier for developers to then deploy this code to production.
Pro Gitea support
Supports Gitea (Git server).
Cons

Con Proprietary with private project for $30/month
Semaphore is not free and nor is it open source. Pricing starts at $29 per month. However, there is a free option for private projects which have less than 100 builds per month and it's free for open source projects.
Con Does not allow you to configure two projects using the same GitHub repo
Drone.io does not let developers configure two different projects against the same repository. Instead, one must fork that repository into a new one and use that to create a new Drone.io project.
