Nowadays is an adverb used to say something is done now or in the current time. It is one word like heretofore and wheresoever.
Nowdays or now a days are misspellings, even though the origin of the word is a phrase that was spelled as separate words (now a dayes).
A synonym for this term is anymore. It can mean exactly the same as nowadays, or it can mean no longer (e.g., not moving anymore). This is sometimes seen as two words, but the popularity of the single word form has almost completely overtaken the two word form.
Some will say that this is a recent formation and may not be acceptable to some viewers. If there is doubt, or if your writing is meant to be strictly formal, try using another phrase or wording. For all informal communication, the one word is the most popular.
The two word form does still exist in the adjectival form and should be used appropriately.
Do you feel that there is a certain impossibility to “breaking up” nowadays? [Huffington Post]
Nowadays chess players are spoiled with opportunities – there are numerous tournaments held on all continents all year round. [Irish Independent]
“No one is happy … no one gets the hype around him anymore,” the teammate reportedly told TMZ Sports. [NESN]
Anymore, people on the radio generally have a specific purpose in mind. [The Washington Times]
Are there any more honest insurers out there? [Financial Times Adviser]