Composer tributes (classical music)

Musical tributes or homages from one composer to another can take many forms. Following are examples of the major types of tributes occurring in classical music. A particular work may fit into more than one of these types.
Variations.
Variations on a theme by another composer. These are usually written as discrete sets of variations. There are hundreds of examples, including:
Works with other titles.
Many works are based on a theme or themes by another composer (sometimes anonymous or traditional). They range from short pieces to extended major compositions. Sometimes these works are no more than sets of variations under another name, but sometimes they go beyond that. They appear under many titles, including: 
Use of composer's name or an associated name.
Examples of the use of a composer's name as the title of a work include:
Sometimes the name of something strongly associated with the composer is used as the title of a work:
Transcription or adaptation.
Transcriptions or adaptations of existing works for other forces, such as:
Quotation.
Quotation of a theme or themes by another composer. Many examples, including:
Transformation.
Transformation of completed works, such as: 
Synthesis.
Synthesis of fragmentary notes into a conjectural whole, such as: 
Completion.
Completion of substantially written but unfinished works, such as:
Imitation.
Imitation, where a composer deliberately copies the compositional style of an earlier composer, such as:
Dedication.
Dedication of a work to another composer or performer:
Cryptogram.
Musical cryptograms, where the composer’s name is encoded in musical letters. The most famous example of this is the BACH motif, which has been used by over 400 composers in tribute to Johann Sebastian Bach (Bach himself used it more than once in his own works). Other examples include: