Test Collab does offer REST API making almost all the features accessible.
Anyone with the knowledge of HTTP request and response handling through JSON and a programming language can very well take advantage of the API that offers features ranging from adding and modifying test cases to managing projects.
Major entities covered for the purpose are:
Test Executions, and
More details on the Test Collab REST API are available at - http://support.testcollab.com/index.php?pg=kb.book&id=6