Ranked in these QuestionsQuestion Ranking
Pro Free for open source
Coveralls offers unlimited free support for open source projects.
Coveralls is older than Code Climate and already supports 21 languages. It also seems like it's the most popular given how new some of the other services are, which is great for support.
Con Terrible support
Con The user interface is hard to understand
Con It's defective and integration doesn't work properly
Con Last product update in 2016
Con No support for common coverage report stadards
They accept their own format over their own HTTP API. Other services allow the uploading of standard reporting formats and parse them internally.
Con Poor tooling
Depending on your language the tooling is practically abandonware.