So far, I have tried many online tools. However, I will list you some of the tools that helped me a lot.
SQLDBM offers you an easy, convenient way to design your database absolutely anywhere on any browser, working away without need for any extra database engine or database modelling tools or apps. Use SQLDBM to design and manage both large and small databases and data models on the fly. All while incorporating any needed database rules and objects such as database keys, schemas, indexes, column constraints and relationships.
Price: Free
A free 14-day evaluation copy can be downloaded. The purchase price includes 12-month support. After the first year, support can purchased for 35% of the original license price.
"Discounted licences are available for qualified Academic users and free licenses are available for qualified Open Source Software (OSS) Developers."
Price: $400
A recent upgrade offers significantly improved features. Supports Forward and Reverse Engineering for about 20 different Databases.
Price: Offers a Free download or starts at $259 to buy.