Working!! first starting airing in 2010, and consist of 2 other sequels. The 2nd season aired soon after, in year 2011, while the 3rd season aired in 2015.
Working!! Has a fixed set of characters which they focused on. Side characters are then slowly added on throughout the next 2 seasons as they go deeper into the story line. The anime is also popular for their love lines (mostly that one love line which everyone likes). The anime has a very structured development and the story line flows very well (even though it's a comedy.)
In 2016, they decided to air another anime called 'WWW.WORKING!!', which is an alternative setting to the main series - still unsure if it's the future or the past (or if it's even related to the parent series at all). It's taken from the web series of Working. The new series consist of a whole new set of characters which seemingly resembles the parent series.
The characters all have a new unique point themselves, and doesn't clash with anyone in the parent series, which makes it seems like a whole new series. But the strong similarities in the relationships between the characters makes it connected.
Firstly, in Working!!, Takahashi's family was one of the main points in season 2 and 3, which they actually expanded a lot throughout the whole series, and his family was also the cause of his obsessions with small and short things (or people). Which was one of the reasons why he started working in Wagnaria - because he couldn't refuse his cute senpai who begged him to work at Wagnaria.
In the WWW series, it started out with Higashida's - whose voice actor , Nakamura Yuichi, also voiced one of the side characters in the original series - reason for finding a part-time job. It was due to his dad's business failure. Higashida's family was also shown throughout the whole series, and played a huge part in the anime.
While in the first Working!! series, they focused more on how the characters get together (which may require more patience from the viewers), the WWW characters get together pretty early in the anime (not because of love), and they show more of their progressed in their relationships.
In the original series, it can be seen that all the characters interact with each other, while in the WWW series, the characters are paired up and they usually only interact within their pairs.
Overall, the original series focuses more on the character developments (where the 'slice of life' genre is stronger here), while the WWW series gives a more flexible view to the story, while more jokes (where the 'comedy' side in stronger here). They are both wonderful series, and I recommend viewers to watch both.
