The number of patents that reference #IOTA. "In total, 111 patent applications from 44 companies have been published (up to 2019)" - this is what real ecosystem development looks like...
If you filter cryptocurrencies by Proof of Work algorithm, and remove BTC fork clone coins. You would get the next Top 10 cryptocurrency list:
1 $BTC
2 $LTC
3 $XMR
4 $ETC
5 $DASH
6 $DOGE
7 $ZEC
8 $DCR
9 $RVN
10 $DGB