It's available electronically, it needs only one page from D&D 3E or the d20 SRD for true standalone, and it has a functional ruleset...
Viable? uncertain.
Available? absolutely. $35 CD gets you all of it, and most of it is CT 2E compatible dual-stat.
Useful for converting D&Ders now, given 5E? not so much.
Useful for converting PF 1E players? kinda, but a few important things (esp skill point allocation) work differently.
Useful for converting PF2E players? not so much.
Could it be revised for 5E compatibility? Sure! Except for the MGT license in effect...