OpenTripPlanner (OTP)  is an open-source multimodal trip planner currently under-development and in a beta test phase for several regions in the United States and internationally.
The multi-modal aspect of the trip planner means that it is possible to plan many types of trips using the trip planner, including transit-only (with walking), bike and transit, driving and transit (utilizing park and ride locations), bike-only, walking-only, or driving-only trips.
The multimodal bike/transit trip planning features of OpenTripPlanner are especially useful for areas with many bike-and-ride customers, or bicycle facilities. Some transit services offer park and ride services, for which OpenTripPlanner would also be useful. Other benefits of OpenTripPlanner include the opportunity to closely control trip planner results and the way in which information is presented to customers by virtue of the customizability of open-source software.
A regional-implementation approach for OpenTripPlanner seems to offer the greatest benefit for transit passengers and agencies in a region, as many agencies can pool resources to create a trip planning product that works across multiple connected systems. To pursue a regional trip planner approach, transit agencies would need to identify and work with partner agencies. An ideal lead agency should have information technology and/or GIS staff experts to manage the implementation process.
The non-profit organization OpenPlans provides a free “OTP Deployer” service  for agencies to preview OTP for their transit network. It is necessary to have GTFS data to upload to use this service. $5,000 is an estimated baseline cost for basic deployment and maintenance of OTP for one year. This estimate assumes 25 consulting developer hours at $100/hr, and a hosting cost of $2,500.
Mobile client (Android)
The Center for Urban Transportation Research at the University of South Florida developed an open-source Android client application for querying OpenTripPlanner. It is designed to interface with any OpenTripPlanner server via the OTP RESTful API. More information is on the github project page (github.com/CUTR-at-USF/OpenTripPlanner-for-Android)
Known OpenTripPlanner-based Deployments
- TriMet - http://ride.trimet.org/#/
- Valley Transit Authority - http://tripplanner.vta.org/planner
- New York State Department of Transportation - https://www.511ny.org/
- Arlington County Commuter Services - http://www.carfreeatoz.com/
- Helsinki Regional Transport Authority - https://digitransit.fi/en/
- Municipal Transport Company of Valencia S. A. U. - http://www.emtvalencia.es/geoportal/?lang=en_otp
- SMTC - http://www.metromobilite.fr/
- STAR - https://itunes.apple.com/us/app/starbusmetro/id899970416?mt=8
- ZTM Poznan - http://poznan.iplaner.pl/
- ZTM Lublin - https://www.ztm.lublin.eu/
- Adelaide Metro - http://jp.adelaidemetro.com.au/opentripplanner-webapp/
- ViaggiaTrento & ViaggiaRoverto - https://play.google.com/store/apps/details?id=eu.trentorise.smartcampus.viaggiatrento
- Smart Campus Project - http://www.smartcampuslab.it/
- Ruter - http://ruter.no/reiseplanlegger/
- USF Maps - https://maps.usf.edu/
- Regional Transportation District - http://www.rtd-denver.com/
- Cherriots Salem-Keizer Transit - http://cherriots.org/
- SMRT - http://journey.smrt.com.sg/
- Sound Transit - http://www.soundtransit.org/tripplanner
Known Unofficial OpenTripPlanner-based Deployments
- ViviBus Bologna - http://bologna.vivibus.it/
- Singapore Nextride - https://itunes.apple.com/us/app/nextride-singapore-public/id565103559
- BJCTA - https://www.bjcta.org/
- Tranzmate - http://www.tranzMate.co.il/
- OpenPlans. "Introducing OTP Deployer." Accessed August 1, 2012 from http://opentripplanner.com/2012/06/introducing-otp-deployer/