This project got started out of a work from a Danish friend, Lars-Bo Vanting, at the time we worked together back in 2005.
Initially it was only based on Tables, Views and PL/SQL. The current version has expanded on the basis and added a web GUI (based on the excellent open source project Open BlueDragon.)
This version of OTR does a bit more than just collect tablespace usage on a weekly basis. It monitors each database instance every 5 minutes and reports back if a tablespace is getting full and one can directly act on the upcoming problem, extend a tablespace or add a new tablespace file without the need to do this over the Enterprise Manager or manually.