River Information Services

Inland Electronic Navigational Chart (IENC) means the database, standardised as to content, structure and format, issued for use with inland electronic chart display and information systems operated onboard of vessels transiting inland waterways.
An IENC is issued by or on behalf of the authority of a competent government agency, and conforms to standards initially developed by the International Hydrographic Organization (IHO) and refined by the Inland ENC Harmonization Group.

ENC Croatia - LINK                            ENC Serbia  - LINK

Software: SeeMyENC
https://www.sevencs.com/see-my-enc-download/ 

An IENC contains all the chart information necessary for safe navigation on inland waterways and may contain supplementary information in addition to that contained in the paper chart (e.g. sailing directions, machine-readable operating schedules, etc) which may be considered necessary for safe navigation and voyage planning.