Secunia PSI is very good at what it does. I am not aware of any functional alternatives but I also lived without Secunia PSI for several decades as I tend to apply updates to anything and everything religiously as they are issued.
There are almost certain to be other alternatives that are similar, though.
+1!
Secunia PSI has been a major part of my security portal dating back to the early Windows 7 years (PSI version 2).
This is going to be a great loss, as it automatically keeps browsers, Flash Player, Java & other software up to date & also notifies one of missing updates. Belarc Advisor is good for the latter, although creates a few false alarms (updates sometimes doesn't apply to one's OS), so it's not great.
I for one will be missing Secunia PSI, as have several computers to upkeep & have installed the app on most every computer worked on for others, am sure that the phone will be ringing once EOL comes. The bottom line is likely that Flexera are likely concentrating on their business customers (there's no 'going out of business' notice) & leaving it's free customers to fend for ourselves. Personally, I see this as a huge mistake, my reasoning being that many business computers (not associated with Flexera) aren't connected to the Internet, this could have major security implications for us all.
There is not a single positive I can see in this action, other than Flexera are waiting until after the annual US tax season to drop support. Yes it'll save some bandwidth traveling to & from the servers of Flexera, yet they likely have an unlimited plan anyway. They likely want more paying customers, it's a business decision, not a personal one & will prevent (some) businesses from 'freeloading'. Secunia PSI was intended to be free for home/student usage, not for small to mid size businesses looking to pinch pennies to beat the system, am sure this played some factor, whether or not they'll publicly admit so. The below are what they're supposed to be using.
https://www.flexera.com/enterprise/products/software-vulnerability-management/software-vulnerability-manager/
Those with certain security software may see updates, last I recall, Avast done this for their free users. Don't know if it was a time limited offer or what, as I've ran Avast very little since MSE became a smashing success in the early Windows 7 years and when did, didn't install the optional component.
There's also the FileHippo App Manager, link below (formerly FileHippo Update Checker) that we can install & run a manual scan with, a small piece of software w/out any 3rd party bloat. It shows updates to popular software that Secunia doesn't, although it's best to have Unchecky installed prior to downloading & installing software from their site. While not all of their software ships with garbage (where I've been obtaining Macrium Reflect Free from for a decade or longer w/out any junk), it's best to be prepared & still check through any boxes slow, as sometimes Unchecky also misses a few of these offers or PUP's.
https://filehippo.com/download_app_manager/59899/
Bottom line, we need to keep our software updated, no matter how we have to. I'll do what's needed to keep my computers updated, and save the installers for quicker updates of all. There's no such thing as under emphasising the importance of having all software on one's computer up to date. Newer versions are often patched to prevent remote control execution & other exploits, to include pathways to Malware/Ransomware attacks. The bad guys never sleeps, it takes a lot of work by the good ones just to keep up, getting ahead is even harder. Running old software can pose great risks to our security, if needed, I recommend to use on a spare machine, not the one used for email, transactions & anything of importance.
Bleeping Computer maintains a list of popular software choices, to my recollection, have never had issues with any 3rd party bundles being installed. Others, such as Adobe Flash for Firefox, has to be manually downloaded from their site, as does Java. It's recommended to uninstall older versions of Java before installing the latest,, since I've lived Java free for 5+ years, don't know how Secunia PSI handles the updates to this software choice. Used to be, most all computers shipped with it preinstalled, today this is unusual, because over 95% of computer users doesn't need this package installed, is now considered a liability if not needed.
Final words on Secunia PSI, am glad that it was mentioned here, otherwise may had never known until the software no longer worked. I made it w/out Secunia for over a decade prior to discovery & will survive in the post era of their no longer free to use software.
Cat