Good day! I wanted to know, when will JetBrains publish post about the technical details of this editor(what programming languages, frameworks, etc. were used)? I am personally interested in how JetBrains ended up with JVM software with a lightweight and beautiful UI?
You can check it out yourself. IntelliJ is mostly open source, with some additional proprietary closed-source plugins included in the paid IDE’s. Source code here: GitHub - JetBrains/intellij-community: IntelliJ IDEA Community Edition & IntelliJ Platform
OP asked about Fleet, not IntelliJ.
If you go to https://www.jetbrains.com/fleet/ and scroll down, they have some information as to when the code will be open source:
JetBrains says details will be released in the following months.
What they have said is that it is being built with Kotlin using Skia (via Skiko):
Hope that clarifies your question