To register - go to Meetup
API's
Blocktrail
Bitcore
bitpay
insight.is
blockchain.info
coinbase.com
Bitcoin Libraries
Bitcoin Core
bitcoinj
bitcoind
bitcoinJS
libbitcoin
bitcore.io
btcd
Toshi
Blockchain Explorers
blockchain.info
blockr.io
biteasy.com
https://www.blocktrail.com/BTC
Guides
bitcoin.org
bitcoinbook
Other learning resources
Mastering Bitcoin
http://testnetwallet.com
telecomnews.co.il - previous bitcoin hackathon
github - previous bitcoin hackathons
https://github.com/DavidJohnstonCEO/DecentralizedApplications
Blocktrail
Bitcore
bitpay
insight.is
blockchain.info
coinbase.com
Bitcoin Libraries
Bitcoin Core
bitcoinj
bitcoind
bitcoinJS
libbitcoin
bitcore.io
btcd
Toshi
Blockchain Explorers
blockchain.info
blockr.io
biteasy.com
https://www.blocktrail.com/BTC
Guides
bitcoin.org
bitcoinbook
Other learning resources
Mastering Bitcoin
http://testnetwallet.com
telecomnews.co.il - previous bitcoin hackathon
github - previous bitcoin hackathons
https://github.com/DavidJohnstonCEO/DecentralizedApplications