I already wrote an article about Internet Download Manager and other download alternatives (commercial ones), there is only Download Master (free) or from the same developer team Internet Download Accelerator but what are the open source alternatives? Well, basically only Persepolis Download Manager which is really able to compete against IDM & Co.
Persepolis Download Manager (PDM) works with all operating systems like Windows, Linux/GNU and MacOS which makes the program really unique because not other GUI based open source program does support so many different OS types, this is due the fact that the program is written in PYQT5 and build around the aria2 download engine.
PDM is open source and hosted on GitHub, there is also an official landing page (homepage) also hosted via GitHub which is available here. The official download link to the latest version is always available here. Their official FAQ explains already a lot of things, like if there is a Browser extension or how to download certain files from e.g. YouTube and the official Wiki page answers all other questions.
Chrome, Firefox and Opera are the supported Browsers, other Browsers like Edge or Internet Explorer aren’t supported because there not available for other Operating Systems or simply won’t support extensions (like eg. IE).
The program is constantly under development and gets improved with bugfixes and new features, a torrent download function is not planned, the developer explained that there already other or better solution for this.
I would’t say that the program is a replacement for IDM because some functions are missing due copyright reasons or ‘Store’ (extension) problems. But IDM is only avaible for one platform, so the overall point here goes to PDM.
There well know problems like translation issues and others which are all reported on their official bugtracker. The program itself has a huge potential and I think it simply needs more supporter to add the missing functions like an automatically ‘grabber’/scheduler and such advance functions - but the rest is already covered and you can download video-, audio- and program-files without any problem.
What is missing?
Downloading files are important because we are doing it daily, the integrated Browser mechanism is fine but it lacks support of some basic function and it ends up with installing other extensions or programs like IDM or PDM. Persepolis has a good potential to become the number one download manager after IDM and JDownloader. JDownloader is often half-functional or blooded with ads (can be manually disabled) and people prefer lightway programs like IDM instead - but this solution cost money so a lot of people pirating the program which is not good, especially if you like the program you always should consider to buy it. So the gap is filled with PDM which has it’s weaknesses but nothing is impossible to fix. Because of the mentioned arguments Persepolis Download Manager gets my recommendation.