Based on list of Regular Expression Engines from https://en.wikipedia.org/wiki/Comparison_of_regular-expression_engines

Engine	Language	Flags	Note
Boost.Regex	C++	imsx
DEELX	C++	imsg
Glib/GRegex	C++	imsx
GRETA	C++		Could not find documentation.
Gregex	RTL, HLS		Could not find documentation.
RXP	RTL		Could not find documentation.
Hyperscan	C++	imsx	Based on PCRE.
ICU	C, C++	imsxw
Jakarta/Regexp	Java		Deprecated project. Could not find documentation.
java.util.regex	Java	imsxduU	d flag is UNIX lines mode (only use \n for ., ^, and $).
Jregex	Java	imsxuX
MATLAB	MATLAB	imsx
Oniguruma	C	imxWDSPy	D makes \d match only ASCII digits.
Onigmo (Oniguruma-mod)	C, Ruby	imxdau	Fork of Oniguruma. d is Default compatiblity mode for Ruby 1.9.3.
PCRE	C, C++	imnsxx
Qt/QRegExp	C++		No character-based flags that I could find.
RE2	C++	imsU
RGX	C++		Could not find documentation.
SubReg	C	iI
TPerlRegEx	Object Pascal	imnsxx	Wrapper for PCRE.
TRE	C	inrU
TRegExpr	Object Pascal	imsgxr
XRegExp	ECMAScript	imguynsxA
APL	APL	imsx	Based on PCRE.
C++ 11	C++
D	D	imsxg
Go	Go	imsU	Based on RE2.
Haskell	Haskell	imnsxx	Multiple implementations including PCRE.
ECMAScript	ECMAScript	imsugy
Julia	Julia	imsxa
Lua	Lua		No character-based flags that I could find.
Mathmatica	Mathmatica		No character-based flags that I could find.
.NET	.NET	imsxn
Nim	Nim	imnsxx	Uses PCRE.
Ocaml	Ocaml		No character-based flags that I could find.
Perl	Perl	imsxxpaadlun	d enables legacy problematic behavior.
PHP	PHP	imnsxx	Uses PCRE.
POSIX C	POSIX C
Python/re	Python	iLmsux
Python/regex	Python	iLmsuxV0V1
Rust	Rust	imsUux
SAP ABAP	SAP ABAP		No character-based flags that I could find.
Tcl	Tcl	imsxnbcepqtw
Wolfram	Wolfram		No character-based flags that I could find.
XML Schema	XML Schema		No character-based flags that I could find.
XPath 3/XQuery	XPath 3/XQuery	imsxq