The most important changes:

*** common ***
* Change structure of sources tree.
* Remove embedded libraries where it is possible.
* Use new features from C++17.

*** libeiskaltdcpp ***
* Add IPv6 support.
* Improve Lua support.
* Use new API from OpenSSL 3.0.

*** eiskaltdcpp-qt ***
* Stop support of Qt 4.x.
* Use new features from Qt >= 5.12 and C++17.
* Add support of Qt 6.x.
* Rewrite spell checker from Aspell to Hunspell.
* Full code refactoring using strong QA rules!
* Add dialog widget for debugging Lua scripts.
* Add search panels to widgets:
  * Finished downloads
  * Finished uploads
  * Search spy

*** eiskaltdcpp-gtk ***
* Remove GTK+ UI completely.

*** eiskaltdcpp-daemon ***
* See: eiskaltdcpp-cli/TODO

*** eiskaltdcpp-cli ***
* See: eiskaltdcpp-cli/TODO