Hikes on the web

Lower Austria (Niederösterreich)

https://www.google.com/maps/d/viewer?mid=1mK7f_ErupgMDeX04VVnE0xgZ7as
Lots of hikes in Lower Austria, with descriptions from the newspaper "DerStandard".
 

Südtirol (Italy)

https://www.suedtirol.info/de/informationen/suedtirol-apps/suedtirol-trekking-guide
An app with lots of hikes and good maps

Maps

http://www.austrianmap.at
Online map for all of Austria - unfortunately not very user friendly but the maps are good

https://www.outdooractive.com/de/tourenplaner/
Great maps for hiking, for all of Europe

http://umap.openstreetmap.fr/de/
Draw your route into a map, very easy

http://www.openandromaps.org
Maps for your Android Map App

http://www.freytagberndt.com/
A very good shop for buying maps for Austria, Europe and around the world. Also lots of travel guides, and outdoor sports guides, including a lot in English. Online or at their shop, Wallnerstraße 3 in Wien 1.

Apps

http://www.oruxmaps.com
The best App I know for mapping. The last version is only available on this website, not on Google Play.
 

Climbing/Via Ferrata

http://www.bergsteigen.com/
A comprehensive guide to just about all climbing routes, via ferratas, skitours and much much more in Austria. The site is in German, but with help from google translate and the topos and photos, you can get some good ideas for your next trip