It appears that Strugatsky brothers have written a stage adaptation of Hard to be a God, named Without Weapons or A Man from a Distant Star. Wikipedia claims that the play "reveals previously unknown details" about the world of Hard to be a God.
What exactly does the play add? What are the differences between the novel and the stage adaptation?
First of all, as is usual with user-generated content, Wikipedia has glaring errors here. Here's what English Wikipedia page that caused you to ask the question says:
Without Weapons (Без ��ружия, Bez oruzhia) also known as A Man from a Distant Star (Человек с далёкой звезды, Chelovek s dalyokoy zvezdy) was a play created by the Strugatsky brothers themselves in 1989. It roughly followed the plot of the book and revealed several previously unknown details. Certain characters were also combined together for the sake of brevity. The play was most likely created as a reaction to the Fleischmann film.
This is ALL wrong:
The play's first version (see below) was created (finished) in 1976; and was created not as reaction to 1989 Fleischmann film, but in response to 1966 request by Lyubimov, a famous Taganka theater director.
Even a second version, despite being published in 1989, was actually written in 1980s and had nothing to do with Fleischmann.
It's not a big surprise that "revealed several previously unknown details" is also way wrong.
The play isn't some further elaboration of book canon, the way J.K.Rowling's ahem later "works" are. It's merely a theatrical play "based on" the book.
The play was not even "non canon" for the book - it wasn't even "canon" for Strugatsky Brothers themselves. They hated it; and refused to include it in published complete works.
The only "details" the play reveals are things that are deliberately different from the book for play purposes (see below).
Second of all, you should be aware that there are two separate, very different versions of the play:
First 1976 "Человек с далёкой звезды (Без оружия)" / "Man from a distant star (without weapons)" version.
An interesting tidbit: this was written for the famous Lyubimov's theater, with Rumata to have been played by Vladimir Vysotsky (for English speakers, imagine a mix of Bob Dylan and Sir Christopher Lee as far as popularity/cultural influence :)
This version is about 50% shorter; and has a very different backstory (see below)
Second version: "Без оружия / Время серых" ("Without Weapons" / "The Time of the Grays") published in 1989 and more famous.
First of all, let's start with main differences between the second later version, and the book:
Kira gets involved with jealous triangle with Dona Okana
The attack on Rumata's house happens because Kira blabs to visiting Okana things about Rumata and Budakh that she relays to Don Reba; coupled with the fact that Dona Okana is jealous of Kira.
В финале гибнут не только Кира и Уно, но и Арата Горбатый и сам Румата
In the epilogue, not only Kira and Uno die, but Arata the Humpback and Rumata himself die.
Кира гибнет не от арбалетной стрелы, а от метательного ножа.
Kira isn't killed with a crossbow bolt, but with a throwing knife
Барон Пампа дон Бау в романе — потомственный барон и друг Руматы, а в пьесе — его преемник.
Baron Pampa is not Rumata's aristocratic friend; but instead his successor.
Будах в пьесе — колдун, поэт, мистификатор и учёный, в то время как в романе — лишь выдающийся врач.
Dr. Budakh is a wizard, poet, mystic and scientist; whereas in the book he's just a doctor.
Румата: Будах? Тот самый? Будах Арканарский?
Кондор: Тот самый знаменитый Будах. Математик и астроном.
Румата: И еще немножко поэт, немножко колдун, немножко мистификатор, как я понял... почему он окопался в "Серой Радости"?
Related to the last two bullets, Dr Budakh in the play actually absorbed a lot of features of the book's Baron Pampa (he's huge, likes to fight and drink).
In the book, Marshal Totz lived 300 years before the events (Rumata says so in his musings after meeting Kiun). In the play, Totz is alive and in charge of attacking Arata's peasant mutiny.
Кира в пьесе — дочь трактирщика и сестра Абы.
In the play, Kira is daughter of pub owner and sister of Aba
Дона Окана не гибнет в пьесе.
Dona Okana stays alive in the play
Дон Сатарина становится доной в пьесе.
Don Satarina became female Dona Satarina; and I don't think there's any backstory about selling torture collection.
Second of all, let's look at the differences between the first original play version and second version (summarized here):
~ 50% shorter
The action happens on Giganda (instead of unnamed planet where book's Arkanar kingdom is on) - the planet which is a setting for a different Noon universe novel, "The Kid from Hell"
The historical period is a later one, with widespread muskets and other fire arms.
The prologue / backstory is vastly different.
The reviewer in linked page likened it - not without cause - to a mix of "Hard to be a God", "Inhabited Island", and "A guy from Purgatory"/"The Kid from Hell".
Servant boy Uno is actually Kira in disguise.
