So, i thought about massive multiplayer game, and start a simple to implement project, with following features:

1. Unlimited 2D Map (minecraft style generation)
2. Player can place/remove blocks like simple building block or weapon turret (currently keys 0..9 , or click on bottom toolbar, or drag items from bottom toolbar)
   2.1. Firstly player should place “core block” at any applicable place (key ‘C’)
   2.2. Next blocks should be placed “side by side” with already build blocks, i.e. block should have at least one common side with block on the map.
   2.3. Blocks can be build only on some kind of terrain (currently build impossible only on water)
3. AI/firing/damage calculation is server based, its against cheats, but cause some traffic limitation.
4. Server split players into groups by areas they can see, so huge amount of players supported (if not, i`ll rewrite server side on C++), i try to be very care about traffic
5. In nearest future i finish implementing NPCs castle generation.

How to try (game under development!, your progress could be lost):

1. go to "stilker.sknt.ru" site preferably by PC (works with webgl2 enabled mobile browsers too)
2. Login as any combination of symbols, no password required at the moment
3. scroll map with mouse, press buttons 0..9 to place blocks or ‘c’ to place 'core" block, mouse wheel to zoom, or click/drag items on building on toolbar
4. Open another browser/tab with "stilker.sknt.ru" , login as other player, build blocks which will be fight with other players blocks, or just invite friends.

IMPORTANT: server hosted on RaspberryPi3 microcomputer, not sure how much players it can handle, will reboot server if noticed about problems.

BTW: project written on pure JS(+node)/WebGL, so starts instantly =)

ASSETS:
"Tower Defence Basic Towers" by Nido licensed CC0: https://opengameart.org/node/114170​
and