Siril Alternatives
Siril is described as 'astronomical image processing tool, able to convert, pre-process images, help aligning them automatically or manually, stack them and enhance final images' and is an app. There are five alternatives to Siril for Windows, Linux and Mac. The best alternative is DeepSkyStacker, which is free. Other great apps like Siril are Regim, IRIS, PixInsight and Fitswork.
DeepSkyStacker is a freeware for astrophotographers that simplifies all the pre-processing steps of deep sky pictures.
Regim makes some processing steps that are unique to astronomical images a bit easier. These steps are calibration (dark and flat), deblooming, registration, combination, color calibration, gradient removal and some more.
IRIS is an astronomical images processing software.
Main features
Image aligning and stacking, calibration, correction and enhancement, DSLR camera control.
PixInsight - Advanced Image Processing. PixInsight is a modular, open-architecture, portable image processing platform available for FreeBSD, Linux, Mac OS X and Windows.
Fitswork is a windows image processing program, mainly designed for astronomic purposes. It contains batch processing, histogram functions, many filters, etc. Fitswork works entirely in floating-point arithmetic.