ALGOL X was the code name given to the programming language

Programming language

A programming language is an artificial language designed to communicate instructions to a machine, particularly a computer. Programming languages can be used to create programs that control the behavior of a machine and/or to express algorithms precisely....

 which the Working Group 2.1 on ALGOL of the International Federation for Information Processing

International Federation for Information Processing

The International Federation for Information Processing is an umbrella organization for national societies working in the field of information technology. It is a non-governmental, non-profit organization with offices in Laxenburg, Austria...

 was to develop as a successor to ALGOL 60

ALGOL 60

ALGOL 60 is a member of the ALGOL family of computer programming languages. It gave rise to many other programming languages, including BCPL, B, Pascal, Simula, C, and many others. ALGOL 58 introduced code blocks and the begin and end pairs for delimiting them...

. It attempted to find a "short-term solution to existing difficulties".

"... the Algol 60 devotees had not been idle... they set out to eliminate the dreaded Remaining Trouble Spots.
They called their Algol 60 "Modified". - R. de Morgan. - Jul 1977 Title "The Algollers"

One ALGOL X compiler is known to have existed, it was written with the AED-0 (Automated Engineering Design) System by Douglas T. Ross

Douglas T. Ross

Douglas Taylor Ross was an American computer scientist pioneer, and Chairman of SofTech, Inc.. He is most famous for originating the term CAD for computer-aided design, and is consider to be the father of Automatically Programmed Tools a language to drive numerically controlled manufacturing.-...

 of MIT.

Example class definition: (An extract from AB26.2.2)
class expression is constant (real value) ora variable (string printname)
ora class pair is (sum ora difference ora product
ora quotient)((expression) left operand, right operand, derivative);
Example class usage:
(expression) X; (constant) Y; (pair) Z; (product) Q;

X := Y:= constant(10.5);
Z := Q := product(variable("ALPHA"), constant(2.), constant(2.))

The ALGOL Bulletin

ALGOL Bulletin

The ALGOL Bulletin was published by the Association for Computing Machinery regarding the ALGOL 60 and ALGOL 68 programming languages from March 1959 till August 1988.-Time-line of ALGOL Bulletin:- References :...

 on ALGOL X

• AB21.3.1 - G. Seegmuller: Some proposals for ALGOL X http://archive.computerhistory.org/resources/text/algol/algol_bulletin/A21/P31.HTM
• AB21.3.2 - Joachim von Peschke: Proposals for ALGOL X http://archive.computerhistory.org/resources/text/algol/algol_bulletin/A21/P32.HTM
• AB22.3.2 - J.N. Merner: Own concept and ALGOL X http://archive.computerhistory.org/resources/text/algol/algol_bulletin/A22/P32.HTM
• AB22.3.10 - M. Woodger: ALGOL X, Note on the proposed successor to ALGOL 60 http://archive.computerhistory.org/resources/text/algol/algol_bulletin/A22/P310.HTM
• AB25.0.1 - ALGOL Bulletin - ALGOL X http://archive.computerhistory.org/resources/text/algol/algol_bulletin/A25/P01.HTM
• AB26.2.2 - Douglas T. Ross
  Douglas T. Ross
  Douglas Taylor Ross was an American computer scientist pioneer, and Chairman of SofTech, Inc.. He is most famous for originating the term CAD for computer-aided design, and is consider to be the father of Automatically Programmed Tools a language to drive numerically controlled manufacturing.-...
  
  : Features essential for a workable ALGOL X http://archive.computerhistory.org/resources/text/algol/algol_bulletin/A26/P22.HTM