You can still get it at the link, but it’s not in active development so it won’t get any more updates.
#Reliable ti emulator for mac update
If it comes back up by the time we update this piece again, we’ll gladly add it back to the list. TI-Nspire: nTris - Update for CX nTris - SDL implementation nMah - Mahjong clone. Mac: nSpiKx - TI-Nspire emulator for Mac.
#Reliable ti emulator for mac skin
Windows: kArmTI - TI-Nspire emulator with skin XML2TXT, XML2LUA, TXT2XML, LUA2XML and 2TNS.
However, the website appears to be down as of the time of this writing. Nspiroid v1.53 is working on my marshmallow (6.0.1) devices, though.