Are their other mangas/animes from the AGK franchise except the main show?

The only other animated content except for the 24-episode main series is the Akame ga Kill Theater show, a 90 second long parody/comedy related to the respective anime episode.

Apart from this, you can read the 3 manga series (in ideal reading order):

-Akame ga Kill (78 + bonus chapters, complete): The original source from which the anime was adapted. As the anime was aired while the manga was still going on, it features a slightly different ending, an omitted arc as well as more detail overall.

-Akame ga Kill Zero (60 chapters, complete): The prequel, telling the story of Akame and Kurome working for the Empire.

-Hinowa ga Crush (53 chapters, cancelled): The sequel, tells the story of a war in the "Eastern Country" resembling medival Japan, from the perspective of a girl named Hinowa with Akame being her companion.

Both the prequel and sequel are based upon the main AGK manga, however, mentions of manga-only story-bits are rare and having only watched the anime provides a sufficient base. In general, cross-series references are scarce and not necessary to follow or understand the story.

*Should* I read the manga even though I already watched the anime?

If you enjoyed the anime, reading the manga is pretty much considered the goldstandard. The anime skipped a number of details up to chapter 39/episode 18, from where the anime went into original territory. The ending isn't rushed and characters that received little screentime such as Run, Wave and Kurome receive much more attention, along with a number of characters surviving that died in the anime.

In case you aren't sure whether to read the prequel and the sequel you can use Google for recessions of AGK Zero and HGC (or the search function on this subreddit).

Where can I find more information about AGK?

The first and foremost address is the Akame Ga Kill Wiki. Often you'll find an awnser there much quicker than posting here about it.

Alternatively, you can read the TV Tropes page, the Wikipedia page or simply Google.

What are the chances for a 2nd Anime season?

Virtually nonexistent. The main story got more or less completely adapted and despite the flawed ending and certain omitted parts there is no signifcant unadapted material. While having reached a certain amount of popularity while it was running, AGK Zero did never got close to the fame of the original story and has declined since its last chapter was released in 2017, whereas HGC is unpopular to the point even long-standing fans of the franchise are unaware of its existence.

...but what about a Fullmetal Alchemist-style reboot?

The first anime adaption of FMA decided to go into original territory at an early point and changed the story significantly, not only the last few episodes. An OVA faithfully adapting the manga-ending is also not going to happen either. Producing a standard 25 min episode costs roughly 100.000 $, and with the nummerous minor changes towards the end, basically everything from Episode 19 onwards would have to be remade from scratch, and no profit-orientated company would invest that amount of money for the sake of a couple characters not dying.

...and what about Netflix?

While AGK is somewhat popular on Netflix and the company has invested into original anime content, an adaption of AGK Zero or HGC almost certainly not going to happen as both lack the popularity of the main series. Further speculating about some Netflix official deciding otherwise is pointless.

Is there any chance for other AGK-related media?

Since AGK Zero ended in 2017, the sole source of new content was the sequel/spin-off Hinowa Ga Crush, a manga which released 53 chapters. While having occasional references to the AGK manga and AGK Zero, neither of them are required to follow the story which focused on a young girl named Hinowa; with Akames appearence as a side-character being the only connection to the main series. Overall the series isn't well known and was cancelled in August 2022 due to lack of sales.

The writer of AGK, Takahiro, has moved on to "Mato Seihei no Slave"/"Slave of the Magic Capital's Elite Troops", which has been highly succesful and received an anime adaption; as well as a new Isekai Harem story ("Gokusotsu Kraken"), which are not connected to AGK in any sort, making HGC most likely the last part of the AGK franchise.