iTerm2
iTerm2 is a terminal emulator for Mac OS X that does amazing things
...To build it, you can compile the Xcode project included, and there is documentation and instructions linked from the project’s README (note: issue tracking is handled via GitLab, as the repository refers issues there). The code is organized into modular parts (resources, UI, helpers, submodules), and the project is actively maintained with many releases and tags.