Web platform - I have been designing novel Web applications that leverage Multimedia techniques since 1998. Most significant work I did is Físchlár family of Web applications which I designed its interface and refined over 5-year period, deployed to campus labs (1999-2005), and conducted a longitudinal user study, published in:
Lee H, Smeaton A.F, O'Connor N and Smyth B. User Evaluation of Físchlár-News: An Automatic Broadcast News Delivery System. ACM Transactions on Information Systems, Vol. 24, No. 2, 2006, pp145-189.

Mobile - Having witnessed the usability crisis(?) of mobile UIs in the early 2000's, I have designed mobile applications that take advantage of automatic processing of information to reduce the interaction burden from the users (e.g. collaborative filtering to selectively show the most useful information first). One of my recent publications on this is the following book chapter:
Lee H, Gurrin C, Jones G and Smeaton A.F. Interaction Design for Personal Photo Management on a Mobile Device. Handbook of Research on User Interface Design and Evaluation for Mobile Technology, IGI Publishing, ISBN: 978-1-59904-871-0, 2008, pp69-85.

Interactive TableTop - TableTop interaction brings in a few very interesting dimensions because it should support co-located collaboration among multiple users: division of labour, workspace awareness and usage coordination (or conflict resolution) need to be designed in, which a single user desktop PC interaction never had. I identified these dimensions and possible design options and designed variations of DiamondTouch TableTop application, published in (among others):
Smeaton A.F, Lee H, Foley C and Mc Givney S. Collaborative Video Searching on a Tabletop. Multimedia Systems Journal, Vol. 12, No. 4, 2006, pp375-391.

Interactive TV - iTV interaction requires a good understanding of yet another set of parameters, most notably the 'lean-back' nature of the use and the input device of remote control. I surveyed all available design wisdom in iTV field and through a long 4-month sketching period came up with strategies that resulted in representing potentially sophisticated Multimedia techniques in a super-simple, lean-back, and attractive TV interface, summarised in:
Lee H, Ferguson P, Gurrin C, Smeaton A.F, O'Connor N and Park H. Balancing the Power of Multimedia Information Retrieval and Usability in Designing Interactive TV. uxTV 2008 - International Conference on Designing Interactive User Experiences for TV and Video, Mountain View, CA, 22-24 October, 2008.

Multi-touch Wall - Large, multi-touch public display is another interaction platform that we will be seeing frequently on the streets, bus stops, shopping malls, parks and city centre areas, changing the urban scenary and what and how people do in public areas. Huge scope of research still needs to be done in this area. My initial application ideas for this were presented at:
Wang C, Lee H and Smeaton A.F. Designing Interaction for a Multi-Touch Wall. 4th Irish Human-Computer Interaction Conference, Dublin, Ireland, 2-3 September, 2010, ISBN: 1872327885.

LifeLogging - LifeLogging may not be considered as a 'platform' per se, but designing an interaction for supporting access (searching and browsing) to typically huge LifeLogging data brings in distinctive design issues in itself. I designed a highly novel interaction strategy that allows a user to browse large amount of SenseCam photos, leveraging our group's automatic indexing techniques. Its interface is summarised in:
Lee H, Smeaton A.F, O'Connor N, Jones G, Blighe M, Byrne D, Doherty A and Gurrin C. Constructing a SenseCam Visual Diary as a Media Process. Multimedia Systems Journal, Special Issue on Canonical Processes of Media Production, Vol. 14, No. 6, 2008, pp341-349.