While Jenkins appears to be pretty dominant in the build server scene in my experience, it is by no means alone. Travis CI is a hosted solution that is popular among open source projects. Buildbot is a build server that is written in, and configurable with, Python. The Go server is another one, from ThoughtWorks. Bamboo is an offering from Atlassian. GitLab also supports build server functionality.
Do shop around before deciding on which build server works best for you.
When evaluating different solutions, be aware of attempts at vendor lock-in. Also keep in mind that the build server does not in any way replace the need for builds that are well behaved locally on a developer's machine.
Also, as a common rule of thumb, see if the tool is configurable via configuration files. While management tends to be impressed by graphical configuration, developers...