Bitcoin and Variants and short forms:

BTC - Bitcoin

LTC - Litecoin

NMC - Name Coin

NVC - Novacoin

TRC - Terracoin

PPC - Peer-2-Peer Coin

FTC - Feathercoin

CNC - Chinacoin

 there are many more but most popular are  listed above. 

Amongst them.

1) BTC  is at one aimed at 21 million bitcoins is reached around the year 2140.

2) LTC

3) PPC

 

Currency	Symbol	Year Est.	Author	Active	Ledger	Website	Value of money supply (May 2013)	Bitcoin-based	Note
Bitcoin	BTC	2009	Satoshi Nakamoto	Yes	P2P network	bitcoin.org	~$1 billion USD[6][7]	Yes	Decentralized ledger currency, SHA-256 proof-of-work
Litecoin	LTC	2011	Coblee	Yes	P2P network	litecoin.org	~$38 million USD[7]	Yes	Scrypt proof-of-work
Namecoin	NMC	2011	Vinced	Yes	P2P network	dot-bit.org	~$4.5 million USD[9]	Yes	Decentralized DNS, SHA-256 proof-of-work
PPCoin	PPC	2012	Sunny King	Yes	P2P network	ppcoin.org	~$4 million USD[7]	Yes	SHA-256 proof-of-work/proof-of-stake

Ref: Wikipedia