Here is an unofficial backup of SigSpec (abbreviation of `SIGnificance SPECtrum'), which is a program that computes a significance spectrum for a time series, developed by Piet Reegen.
SigSpec is primarily used in asteroseismology to identify variable stars and to classify stellar pulsation. The fact that this method incorporates the properties of the time-domain sampling appropriately makes it a valuable tool for typical astronomical measurements containing data gaps.
For Windows build:
No installation required! Just download the link target above. It is ready to use.
For Linux/Unix:
Recommended compilation via
gcc -lm -O3 -o SigSpec SigSpec.c
Online Manual. The PDF version is availble on https://arxiv.org/abs/1006.5081
Please cite Reegen, P., 2007A&A, 467, 1353, if you find this code useful in your research.