Open PHD Guiding
The PHD (Push Here Dummy) Guiding software from Stark Labs is a popular, free package for telescope autoguiding on Mac and Windows. PHD Guiding is designed to be easy to use and to take the frustration out of auto-guiding. The goal of Open PHD Guiding is to bring PHD Guiding to other OS than Windows and enable several developers to work on it, because it's a lot of work for his creator, Craig Stark.
Version 1 kept the same GUI as the original Windows application. It now lives in branches/openphd1. This has the core routines of PHD Guiding as well as hardware that is supported on Linux. Heavy use is made of the INDI platform on Linux.
During a large part of 2013, version 2 was being developed as a major refactoring of the original application, including new GUI, internal structure, support for adaptive optics, and improved Mac OS X compatibility. It now (2013) compiles on Linux, but most of the code supporting Linux devices has been excluded from the release and is not maintained. PHD2 supports only QHY5 cameras, no V4L or INDI. See the documentation wiki page of open-phd-guiding.
Supported cameras sources in v1: V4L2 and INDI. Webcams have been confirmed to work.
Supported mounts in v1: INDI.
Arch Linux AUR packages: version 1 and version 2 (probably very outdated).
Update 2017: version 2 seems to integrate INDI again, and probably that version 1 is deprecated now. Here are compilation instructions.