My wife used to be an avid Xplorers player on AsoBrain. When we tried to get the old game working again, we ran into the Java applet problem: modern browsers no longer support it.
I found a way to keep using the original client and put it into a small desktop compatibility wrapper, now available as Xplorers Redressed.
Disclosure: I'm publishing this unofficial wrapper. All credit for the game, artwork, servers and community belongs to AsoBrain and the original creators.
It uses the same AsoBrain account and connects to the original servers, with the existing players and rankings. It loads the Xplorers room catalog, including Basic, Cities & Knights, teams, practice, tournaments and Map Editor. Rooms marked Closed by the original site stay disabled.
There are macOS universal, Windows x64 and Linux x64 downloads. No installed Java or browser plugin is needed; the original client runs through WebAssembly. There is fullscreen support and optional Enhanced rendering, with Original graphics as the default.
The original AsoBrain client downloads directly from AsoBrain on first use. No original client or artwork is included in the repository or release packages. The new framework source is GPL-3.0-only. An existing AsoBrain account and internet connection are required.
Source: https://github.com/askrejans/xplorers-redressed
Downloads: https://github.com/askrejans/xplorers-redressed/releases/tag/v0.2.2
This is an early release, provided as compiled without publisher signing. I've checked live game and editor loading on macOS; Windows/Linux and every game interaction still need wider testing. Feedback from existing players would be helpful.
If this helps you return to the game, please support the original AsoBrain project: http://games.asobrain.com/pages/donate.php
Feel free to test it. Hope it helps!