General Architecture for Text Engineering (GATE) is an open source software for processing text. It is particularly helpful for annotating text, such as identifying specific people and places, ontology (relationships between concepts), verb tense, and context, including the ability to link your textual data to external information sources as part of the text processing.
GATE has plugins for other natural language processing tools such as Stanford CoreNLP, OpenNLP, and Python. GATE has also developed specific tools for working with the challenges of Twitter data and biomedical data such as PubMed files.
GATE Cloud offers freemium cloud services, including the ability to collect Twitter data and perform sentiment analysis on text you upload or copy and paste into their online tools.