SQLCI is the new enhanced version of sql*plus provided by Oracle SQL Developer Team.
You can see more about that from JeffSmith here
http://www.thatjeffsmith.com/archive/2016/05/oracle-sqlcl-why/ to get access to SQLCI, it is available for download from SQL Developer site.
http://www.oracle.com/technetwork/developer-tools/sql-developer/downloads/index.html go to the bottom of the page, you see this "Command Line - SQLcl - Production".
or if you got latest version of SQL Developer available, go into $SQLDEV-HOME/sqlcl/bin will have "sql"
D:\>cd D:\app\sqldeveloper\sqlcl\bin
D:\app\sqldeveloper\sqlcl\bin>dir
Volume in drive D is RAJESH
Volume Serial Number is E079-099C
Directory of D:\app\sqldeveloper\sqlcl\bin
09/23/2016 07:54 PM <DIR> .
09/23/2016 07:54 PM <DIR> ..
09/16/2016 12:05 PM 12,413 sql
09/16/2016 12:05 PM 2,585 sql.bat
09/16/2016 12:05 PM 398,866 sql.exe
3 File(s) 413,864 bytes
2 Dir(s) 330,668,666,880 bytes free
D:\app\sqldeveloper\sqlcl\bin>sql demo/demo@ora11g
SQLcl: Release 4.2.0 Production on Thu Oct 13 16:42:05 2016
Copyright (c) 1982, 2016, Oracle. All rights reserved.
Connected to:
Oracle Database 11g Enterprise Edition Release 11.2.0.4.0 - 64bit Production
With the Partitioning, OLAP, Data Mining and Real Application Testing options
SQL> select * from dept;
DEPTNO DNAME LOC
---------- -------------- -------------
10 ACCOUNTING NEW YORK
20 RESEARCH DALLAS
30 SALES CHICAGO
40 OPERATIONS BOSTON
SQL>