Chooser is an OS independent multi-functional system for linguistic annotation, adaptable to different annotation schemata. The basic annotation functionalities of the tool are: (i) fast and easy-to-perform selection; (ii) run-time access to information for the candidate senses such as definition, frequency, the associated wordnet synsets with all the pertaining info – synonyms, gloss, semantic relations, notes on usage, form, etc.; (iii) identification of MWEs with contiguous and non-contiguous constituents and supplying information for them at run-time. The basic functions are enhanced with flexible text navigation strategies - forward and backward navigation over: (i) all words; (ii) non-annotated words; (iii) all instances of a word; (iv) all instances of a sense. Finally, а flexible search strategy allowing both exact match search according to word form or lemma, and regular expression search is integrated. The tool interface features a fully-fledged visualization of the wordnet synsets for the candidate senses available for a selected LU through coupling with the system for wordnet development and exploration Hydra. A unified wordnet representation in Chooser and Hydra is implemented. Chooser provides multiple-user concurrent access and dynamic real-time update in the knowledge base, so that all changes, such as newly-encoded synsets, literals, relations, are updated in both systems and made available to all the users immediately.