Long are gone times, when those solutions were known to hackers and productivity junkies. Todo & note management, chat and file storage are tools you have simply no choice but to use it, or you will be used to do again and again the same tasks of synchronising your content between devices and making the same time-consuming mistakes.
Those application owners, despite occupying their own niches, were good players and good value creators. They did not lock data and competed by being useful. More, all of them started targetting, not without successes, business customers, because if individual customers had problems with file synchronisation, then business customers had more of them.
Yet, their time has come to an end, not because those companies did something particularly wrong, but rather because they failed to understand basic laws of supply and demand - small markets attract small players, large markets… attract plenty of competition, and some of that competition is very well founded.
Their business market was recognised by giants such as Google or the completely transformed Microsoft. Indeed, corporations are not good at collaboration and are desperate to change it. The fundamental question is:
Will they prefer a single-vendor solution or will they build their own stacks?
The answer seems trivial. With integration comes robustness and efficiency. Google creates everything by itself. Microsoft sometimes buys companies (Wunderlist) and integrates them, but the end result is the same - one embeddable solution with an acceptable per user bill.
So, if you need Office365, you get productivity suite for free. If you use Google Drive, the same applies. So, why pay twice?
There is no longer room for individual vendors in the productivity suite.
Note how productivity suite serves as an umbrella and isolates customers from particular solutions. If you are not offering a complete suite, you are putting yourself at disadvantage.
Naturally, the decline will not happen instantly. Services like Evernote have customers who had build a lot around them. Think about processes, habits and stored knowledge, you cannot switch it overnight unless it is absolutely necessary (and it is not). The degradation will be slow for a couple of years, until bundled solutions match the functionality. That will be the ultimate end.