Cheat Engine

[ParkourPenguin]

https://www.lua.org/manual/5.4/readme.html#changes
Features:

• Adds a generational garbage collector - even the default settings may work better than the current incremental GC, especially for timers. Some objects might never be collected if a major collection never needs to happen, but at least users shouldn't need to worry about garbage collection themselves or experience seemingly unbounded logarithmic growth in memory usage when using many timers (topic 1 / topic 2)
  
• const variables - can't believe it took this long
  
• to-be-closed variables - allows you to "close" variables when they go out of scope, even on errors (equate w/ RAII); likely a better alternative to the current system of autodestroy userdata objects on garbage collection
  
• Other stuff

Breaking changes (haven't looked into these):

• Precompiled chunks might not be compatible - some people's attempts at obfuscating Lua scripts might break
  
• bitwise operations on strings no longer automatically coerce strings to integers
  
• print() no longer calls tostring() to format its arguments; instead, "it has this functionality hardwired. You should use __tostring to modify how values are printed."
  
• collectgarbage() interface has changed
  
• Some C API and other stuff

[Dark Byte]

It's nice. But not sure if it will get added to CE yet.

collect garbage: CE already does that since 7.0 or so. It has an active collectGarbage and passive garbage collection going on in the background when the GUI is active

const variables: I guess, but not the end of the world to miss it

to-be-closed variables: It's handy but can't be implemented into CE by default as some scripts expect local var declared objects keep existing even after the script has finished. (e.g forms and timers)

Here's an example script showing how automatic garbage collection can be used

[ParkourPenguin]

to-be-closed variables: my bad, I was under the impression they were tied to the value itself and not the variable.
It seems too easy to copy the value and have the __close metamethod called multiple times. I can't think of a good way of reference counting it either (no __copy metamethod)
Some code I was playing around with: