Le Robert Correcteur - time to look elsewhere
A few years ago I bought the Le Robert Correcteur. It is a spelling and grammar checker for French, something that is incredibly useful if one has the intention of writing in French. French is a grammatically complex language and even Le Robert doesn't spot all one's mistakes. But it at least weeds out most of them and will often flag a sentence that it believes to be badly constructed even though it can't pinpoint the precise reason.
It wasn't cheap and came with three licences. I used one on my iMac and one on my MacBook Pro. A while ago I rebuilt the MacBook with an SSD disk and restored from Time Machine. Most things worked but Le Correcteur was having none of it. The licence protection was obviously recognised that something had changed as a result of the upgrade. So I had to use my third and final licence. I've now upgraded to a 2018 MacBook Air. And guess what, I can't even get Le Correcteur to load let alone try to enter a licence key. All attempts to find help on deregistering the app on the old MacBook have failed.
I certainly wasn't going to fork out for another three licences so I decided to consider alternatives. I have used Bon Patron before, a web-based spelling and grammar checker that performs arguably as well as Le Correcteur. I used both the other day to check an email and in fact Bon Patron did slightly better. Although both missed a fairly glaring conjugation error, which might have been because of the way I structured the sentence. Perhaps it wasn't French enough! The only downside to Bon Patron is that is web-based, so without a connection you can't use it. But with almost universal connectivity these days this is perhaps not a major issue.
As a free application Bon Patron suffers a bit from ads, which are of course necessary to fund the project. It appears to be the brainchild of a pair of language enthusiasts. To dispense with the ads you can subscribe, although they make the point that it's more like a donation to keep them going. At €11.99 for a year it's hardly expensive and I've willingly paid up.
They are obviously continuing to develop the software and anonymously use the client submitted texts to help, although you can opt out of your data being used if you have concerns. In this respect Bon Patron is perhaps a better bet than Le Correcteur since being web-based it can be continuously improved while Le Correcteur only receive occasional updates that seem more related to changes to the system OS than improvements to the program algorithms.
Below are screen shots for both utilities showing an intentionally incorrect short piece of improvised French. You will note that Bon Patron correctly highlighted the need to use de after expressions of an unspecified quantity, whereas Le Robert did not. It also picked up the absence of a space after the exclamation mark. Le Robert on the other hand highlighted that marche should be marchent as it refers to les correcteurs. Bon Patron didn't pick this up probably because I placed the verb (marche) before the subject (les correcteurs).
Neither spotted my accidental typing error showing amis instead of mais, but that was perhaps too much to ask even if the phrase as it stands is somewhat nonsensical!
The moral is that these types of utility certainly can help but don't expect them to catch all the faults.