Self-, peer-, and collaborative-assessment aim at integrating learning and assessment and promoting the active engagement of learners in the assessment process. This article presents a web-based environment, referred to as PECASSE, which supports these assessment methods. In addition to the basic functions of uploading learners' activities/reviews, grading/commentary of the work and results presentation, PECASSE supports (a) individual and collaborative elaboration of the activities, (b) review of the activities by one or group of learners, (c) collaboration of authors and/or assessors in synchronous and asynchronous way, (d) submission of the activities up to three rounds after assessors' comments, (e) evaluation of assessors, (f) grouping of learners and assignment of assessors following alternative strategies, and (g) a variety of strategies for setting the assessment scheme applied in the review process. The results from the evaluation of the environment revealed that PECASSE fulfils and facilitates self-, peer-, and collaborative-assessment in a successful way, promotes and enhances the learning process, and students have a positive attitude towards the environment and the assessment methods performed. (Contains 3 tables and 4 figures.)