JavaScript
Math.round(new Date() / 1000)
new Date().getTime()
Java
System.currentTimeMillis() / 1000
System.currentTimeMillis()
Python
int(time.time())
int(time.time() * 1000)
Go
time.Now().Unix()
time.Now().UnixNano() / 1e6
PHP
time()
(int)(microtime(true) * 1000)
Ruby
Time.now.to_i
(Time.now.to_f * 1000).to_i
C#
DateTimeOffset.UtcNow.ToUnixTimeSeconds()
DateTimeOffset.UtcNow.ToUnixTimeMilliseconds()
Swift
NSDate().timeIntervalSince1970
NSDate().timeIntervalSince1970 * 1000
Objective-C
[[NSDate date] timeIntervalSince1970]
[[NSDate date] timeIntervalSince1970] * 1000
MySQL
SELECT unix_timestamp(now())
SQLite
SELECT strftime('%s', 'now')
Erlang
calendar:datetime_to_gregorian_seconds(calendar:universal_time())-719528*24*3600.